If you leave your axle extensions per-plans, and you fly off grass occasionally, or perhaps even if you don't, some day you will very likely snap the bolt that holds the U-1004B axle extension which supports the outer side of the main wheel fairings.  This will most definitely cause a catastrophic fairing failure that may damage your wing and fuel tank nearby.  Replacement axle extensions are available from a variety of 3rd party places that will fix this problem for good.

This problem is both an issue of poor design, and poor piloting.  First, the design leaves much to be desired, as the aft door pin tends not to want to be pulled close enough to the airframe to get the pin to go into the rear pin receiver.  The pin MUST go into the receiver, and all the way through the door frame.  Builders should NOT cut the rack gear per plans, but should cut it in half, giving a little more rack extension, and should guarantee that their pins fit through the door frame fully, 100% past the tapered point on the pin.  Receivers are available from various places as Aluminum, or Delrin, and replacement pin ends are available made from various materials.  The taper is important to pull in the door.  Van's recent Service Bulletin also includes a 3rd latching point with a spring loaded latch. This latch has already failed to hold in at least one RV-10 door that was improperly latched.  If you check out the planearound.com latch, you'll see that it has a center-of-the-door cam that will help pull in the door smoothly, and provide a 3rd latching point that will keep the door shut and still allow a single-hand operation.  This is the ideal.  Van's SB latch would prevent easy discharge of the door, like a previous builder who suffered an in-flight fire due to fuel leak needed to do to clear smoke....save yourself the trouble and just buy or retrofit the planearound.com latch.  Additional I will note that this is largely a pilot induced problem.  Properly latched pins, fully through the door frame, should NOT be a problem for any pilot, but pilots forget to check the pins, and that causes the problem.  Historically, this has been happening much more frequently to BUYERS of RV-10's...people who did not build the plane, build the latch, spend their time online on the forums fully understanding the issues, and generally being as involved as a true builder would be.  Most builders are at least keenly aware of the problem.  Another good idea passed on to me that I left out is that the gap between the door and the pin receivers should be minimal, like 1/8" or less.  Keeping that gap to a minimum would make it much less likely to be able to twist out a door pin and pop it free...if it's in, it's in, and it won't want to come out.

Van's sells you the wrong front wheel....yes, on purpose, because they don't want to stock the proper wheel.  Do yourself a favor and either drop the nosewheel from your order, or BEFORE you install the supplied wheel, send it to Matco and they can re-machine it into the proper wheel half.  If you don't do this, the valve stem can either come dangerously close to the front fork, or worse, will not clear the front fork.  This one baffles me as to why they refuse to just sell you the right part, but it's definitely one to address, sooner rather than later.  Once you buy nice new Leakguard tubes, you'll definitely have issues.

Going hand in hand with the wheel is the front axle.  Van's original axle design was very flawed, and actually caused some people like me to damage their front forks.  Even their improved design, still done on the cheap, doesn't allow you to properly torque the front wheel.  You need to prevent the bearings from rotating on the shaft, so that the bearings rotate at the wheel race, not the shaft.  Matco makes an RV-10 front axle that will fix all of your problems in one shot, and provide a greatly better system.

The plans call for making spacers out of aluminum tubing.  These mate up on one side with Cleveland brake parts, and on the other side, with a large aluminum wheel fairing bracket. Over time and vibration, the aluminum spacers you make will start to mushroom and loosen, accelerating the wear.  There are various fixes, ranging from making the spacers out of steel and putting load-distributing washers on the aluminum fairing bracket, to replacing the entire spacer with much nicer aluminum or steel ones that provide good surface area.  These are available from a couple different vendors.  Either way, don't leave it as stock or a few hundred hours down the line you'll have worn parts and problems.  I'd just buy the spacer replacements and get it overwith.  Also, while you're working in that area, replace the nyloc nuts with all-metal nuts, just like you would in an engine compartment. The nuts in question are in plans section 46, page 4. There is a lot of heat generated by these brakes, especially when the greenhorn RV-10 pilot, not used to castering nose wheels, rides the brakes and uses them too often during taxi turns.  Similarly, builders are advised to use Mil-H-83282 brake fluid with a MUCH higher ignition temp...available at skygeek.com as Royco 782 for only about $10 to do the whole plane.

Although the stock Van's valve has been improved, it's still not nearly as nice as the Andair fuel valve, from both an asthetic viewpoint, and a longevity viewpoint.  It takes a bit of work to install, but you can get it with a knob extension that will better locate the valve so the rear heat SCAT duct goes through the tunnel further away from the valve.  So there are multiple reasons to change it, and the Andair valve is built better and should provide years of service.

First, the quality of the tubing that comes with the kit to use for fuel lines is poor.  You would be better served by 5052-O aluminum.  I've seen many flares tend to crack in certain batches of tubing I was delivered, so either buy better aluminum, or more preferrably, go to braided stainles with Teflon lines.  Bonaco is one vendor but there are others.  You can replace ALL of the lines Firewall Forward with nice fire-sleeved teflon "lifetime" lines very easily now, as vendors are offering full RV-10 "kits".  The brake lines per plans are made from cheesy plastic tubing and would probably never be allowed on a certified plane.  Going to braided lines should basically provide an airframe lifetime of service if you prevent them from chafing.  Also, every connector is a potential failure point.  If you go from fuel valve to tank with a continuous flexible line, you can have fewer connections to worry about, and a far more durable tube than is delivered with the kit.  The only penalty is a little more weight in the case of the brake and fuel lines.  The upside is lifetime and safety.

This is a simple one.  On the filtered air box, they put an alternate air door on the bottom of the FAB.  You rivet it directly to the fiberglass.  If you do this, eventually the rivets will pull through the glass.  Save yourself the headache and make a nice big aluminum backing ring for the inside of the FAB, and sandwhich that fiberglass between them.  It should make it more bulletproof.  Just do it at your earliest convenience but the sooner the better.

If you build the cowl per plans, you will want to change a couple things.  First and foremost, do NOT use hinges on the lower part of the cowl along the bottom, you WILL eventually break the hinge eyelits.  Rivet in aluminum plates with nutplates and use screws and nutplates, or something far more secure, and you'll have something that will last a lifetime.  On the horizontal pins, NEVER EVER run the engine without the keeper hinge-link in place on the front.  Even a short run can make the pin creep forward into the prop.  Also, over time, that front hinge link will wear into the pin, wearing out the hinge link.  Recently I bonded my pin to the link and that should provide a far more vibration free long life, and it also gives a handle to pull the pin out with. There are people who have designed better looking pin caps for those front pins, so my advice is to fix that up front and you'll be far happier.

The reliability of the relays by Ray Allen used in the standard kit for trim has been very poor.  Many people have been experiencing sticky relays, causing them to be unable to trim their plane, forcing a landing with excessive pressure on the stick to maintain proper control.  Ray Allen DID come out with larger, more reliable relays, but there is a far more ideal way to go.  Another problem is that the pitch trim for elevator trim is WAY too fast in cruise.  It's fast enough that if you accidentally have something hold the trim button down, or you have runaway trim, you could easily bend the airplane from a sharp pull-up or push, and cause a huge problem.  The better solution is to swap to the Safety-Trim system.  This in my opinion should be a mandatory item, supplied with the kit.  It provides variable speed trim, engaged with an airspeed switch, that will go to slower speed trim over about 100kts, it also provides runaway trim prevention, only allowing 3 seconds of trim per push, and it provides trim reversal for broken switches, and a panel switch to disable trim power.  It's name says it well, it's "safety" trim, and should provide a far safer operation for your RV-10.  There are also other methods to providing some of this functionality, but most are less complete.  If you have a Vertical Power system, that system builds in some of these features as well.  Regardless of how you do it, speed control is a MUST, yet you DO NOT want slower speed trim at pattern speeds, only in cruise.  Beyond that, I'd definitely avoid any relays that stick.

While my personal opinion is that for 99% of the builders, the standard Van's wheels and brakes will work just fine, there is now a better option.  For all new builders, I'd suggest not purchasing Van's wheels and brakes by Grove, or especially Cleveland, and buy the RV-10 wheel and brake kit from Matco instead.  The brakes are twice as beefy and if you fly in and out of high altitude airports they may be something you'll want.  Long taxi's or aborted takeoffs can really heat up the RV-10 brakes, so you're better off putting more wear surface to the disc.

The Cleveland Brakes that you get with your kit are held on by nyloc nuts.  You probably want to use all-metal lock nuts since these things can heat up.

If you fly IFR, the fuel vent stems can easily become clogged with ice, and once the fuel tank drains and starts to suck a vacuum, you can find yourself unable to supply fuel to the engine.  For people who stay out of the clouds, go ahead and build it per plans.  For those who fly IFR, you may want to consider some sort of ice protection.  I've done this on mine.