I wanted to circle back to this one. This is a small detail, but an important one. Thanks for bringing it to the drawing board! I find myself using this technique in my truck all the time (has a lower 1/2" deep lip at the bottom of the screen). This would be nice on those bumpy trails, but lets be honest a lot of roads aren't that smooth either. I also find myself doing this even while cursing down a nice riding highway when I am needing to click multiple times into something.....I make a few clicks, then look back at the road while holding my finger steady where I last clicked, then return to the where I was on the touch screen to finish.Gloves are great.
I also recall reading that the touchscreens in modern airplanes are designed to be usable in turbulence. For that they have a ridge around the screen to press your fingers against to stabilize your hand (I imagine stabilizing with your fingers and using your thumb, for example). I also think they don't use capacitive touch screens since they are so susceptible to accidental activation ("oops, I just turned of the engines!").
One small detail on the ledge at the bottom of the screen: don't make it with a sharp 90 degree edge, roll it down some.