Going Capless
Regarding the value of having a screw-on valve stem cap, I remember way back in the last century when I lived in Buffalo, NY (much colder than where I now live). A buddy and I washed a car in his heated garage in the middle of winter. When we pulled the car back out into the sub-freezing temperatures, there was apparently some residual water in the one valve stem that didn't have a cap. It froze pretty quickly, and the expansion of the ice allowed air to leak out. In a couple hours, we had a flat tire. It took us some head scratching to figure out what happened. We had to get a hair dryer, thaw out the valve stem, blow the water out, then air it up again. Problem solved, and it never happened again.
Granted, the mechanism of failure wouldn't be exactly the same, but it could be possible for water to freeze when climbing to altitude. Far fetched? Maybe. Would centrifugal force expel any water that was in the valve stem? Probably. But that experience always stuck with me and I ALWAYS put the caps on my cars and my plane.
When I was debating the need for an access door during my build, I read a post on this subject (I think it was from Paul Dye). I don't want to misquote, but he basically said that it's not a bad idea to pull the front half off of the wheel pants and inspect everything in there on a regular basis, which negates the need for an access door to the valve stem. If you have good tubes like the Michelin Airstops, leakage is almost non-existent. So that's what I chose to do. It's not a big deal to pull the front half off.