There was a longer thread on this a few months ago with lots of info.
I would never attempt this in an RV until someone suggested using caulking material instead of grout. Ordinary grout will surely crack and fail due to substrate flexing. Caulk is available in a sanded version in various colors that looks more like regular grout.
That could be a lot of joints to caulk. Keep in mind that once caulk has dried, it does not stick to itself so you need finish it all at once. Also, it skins over in 5 minutes or so and you need to keep moving quickly and clean the excess off as you go. Don't wait until it has dried to clean it off. You should practice on a separate test area first. You need to be adept at laying down the caulk and cleaning it up before putting it down permanently on a finished wall.
I would at the least install a plywood backing sheet of say 1/4" thick and fasten it securely to the wall studs. You can then use Schluter edging to hide the ply and tile edge.
I suppose you could consider installing tiles without grout joints. It's "just" an RV and not a house where it gets grime + water on it 24/7/365.... I'd still install ply backing so tiles don't crack or fall off. Only problem might be that some tiles are not dimensionally consistent from piece to piece.
Gil & Deb & Dougal the Springer Spaniel