If you're looking for under GVWR, you'll have to either go with a very minimalist camper (next to zero options) on a very basic half ton (no crew cabs need apply) or go to a much bigger truck than a half ton. If, on the other hand, you're willing to accept the fact that thousands of trucks, up to and including 1 tons, are running around with truck campers and are over gross but probably not over individual axle ratings which is probably the more important number, then you can be a little more liberal with your camper selection.