Most of Desert Captain's suggestions are worthy of consideration, even if one might reasonably disagree with their severity or importance, but I must very much disagree with this one:
Desert Captain wrote:
Look deep into lockers and behind drawers... find particle board/plywood? Run Forrest run!
I rather doubt there is a class C made that does not use plywood or particle board for the basic cabinet carcasses, possibly covered with melamine or some similar surface. The only other options I know of for RVs is some sort of fiberglass, roto-molded plastic, or sheet metal structure, and I think those are only used for outside compartments or on molded fiberglass trailers ("egg trailers" like the Scamp, Casitas, etc.). Sheet metal would tend to be rather noisy when traveling, I suspect, acting something as a cymbal when going over bumps.
Sometimes there is a framework of wood sticks with think plywood or some similar sheet goods for the wall panels, but that's still plywood/particle board.
A plywood cabinet carcass, if well-made, is sturdy and dimensionally stable and a perfectly sound way of building things. Particle board and pressboard and similar products can also be sturdy and stable, but many disintegrate quite rapidly if they get at all wet, which is a distinct disadvantage.