Oh, you're getting really fancy then! I think for weight bearing areas, then the smaller the tiles the better so they can give a bit. Installing tiles in an RV is a lot different than in a home, as our homes don't get the vibrations of being on the road all the time, unless you live in earthquake territory like I do.
I learned last weekend that if you leave the paper towels hanging in the trailer during transport, that by the time you get to your destination all of them will be on the floor! I had forgotten how bumpy the inside of the trailer gets due to lack of shock absorbers like the towing vehicle has.