Flooring tip: DO NOT USE SELF-STICK VINYL TILE!!!!!
The sun heats it up in an instant, and it expands, forcing the edges of the tile against each other, which causes them to buckle up like crazy all over the place.
If you go with vinyl, use sheet vinyl.
If you go to the Paradigm Shift Gallery (page 8 of the Skoolie.net gallery), you can see what I did for flooring. I put down 3/4" foam, and then put 3/4" plywood. I also installed 120' of CPVC hot water pipe for a radiant heat system that will connect either to the bus's heater system or to a solar collector.
....of course, after I put the vinyl tile down, I read the instructions which said, "do not use with radiant floor heat systems that heat the floor to temperatures higher than 85 degrees Fahrenheit"!