If you have the typical factory arrangement, the acorn nut was simply pulled onto the end of the rivet shaft to provide a finished look inside. However, that would make it hard to take off, since there is probably a bit of a bulge inside it instead of threads.
But, I think it will probably just drop right off when you drill the rivet out, so I would do that first.
What you want to do is drill the rivet, but not enlarge the hole in the camper if you can help it (not the end of the world, but not desirable either). So, use a very thin drill bit that is about the size of the center hole in the rivet top on the outside. Center it in the hole, and then drill carefully at an angle parallel to the rivet shaft. It should drop right out.
Then, see what size the hole in the camper shell is, and size your screw/nut to that hole. You don't want a loose fit, so if you are between two sizes you might have to "refine" the hole in the camper a tiny bit - but not much!
Give it a whirl and let us know how it goes.