If the wall or space behind the intended screw is hallow, then a Molly bolt mount is probably your best bet.
If the wall is styrofoam filled, there's Molly's won't work, neither will expanding bolts, as the styrofoam won't allow the expansion. In that case, glue another board on the surface and use regular screws to hold it in place, or a nail gun with finishing nails. After the glue sets up, then you can mount anything to the additional thickness of wood with a normal wood screw.
If attaching anything to an outside wall, make absolutely sure the screw you are using is shorter than the thickness of your wall.
Attaching a cabinet to the wall, you really need to hit the studs. Although with enough glue (like original Liquid Nails) with a few nail gun finishing nails to hold it in place, will also do the trick pretty well. Just make sure the nails are long enough to go through the cabinet back and the paneling on the wall, but not so long it penetrates the outside wall of the camper.