We put in cheapo 90 cent/ft laminate before the build, and screwed everything down on top of it. Since a bus is only 8 ft wide there's really not enough swelling and shrinking to effect it at all. This is our second year of constant travel in it, and we've had no problems with it other than in a spot where we had the water tank leak for a while before noticing, and that's not damaged very much plus it's under the bed. It was much easier to do that than to cut it to fit around the furniture. That would have been a nightmare, as the edges are prone to chipping as it's being cut.
My build thread:http://www.skoolie.net/forums/f11/build-thread-for-haulin-oats-and-goats-11237.html#post113500
A gal, a guy, three cats, two dogs, one rabbit, and one goat, traveling the country together.