I put marble/granite on couple of RV before and it worked great, especially for beach camping.
But conversion had really strong floor, while vintage Airstream TT had very small floor and I did not put grout between the tiles.
I am considering doing the same on my camper, where vinyl is beaten, but seeing how camper flex when on jacks makes me scratching my head.
Meaning don't think I would put 12" tiles, but 6" with no grout should work fine.
Here is Airstrem if you have the bucket fix, or copy http://i178.photobucket.com/albums/w266/kajtek1/FS%201965%20Airstream%20Safari/IMG_0361.jpg