UPDATED:Tiling the Bathroom With Real Tile Before and After

I used some that sticky stuff for some tile work in my house. I see where it would allow movement and flexing. Considering you are using a silicon sealer instead of a concrete grout, your plan sounds like it might work OK. If you used normal grout, it would probably crumble the first time you moved the camper. Campers have just to much flex in everything. Having done my share of carpentry work myself, I think you've done your homework well.

Keep us posted when you take the camper on the road how it holds up.

Looks nice.