Why not just run a separate extension cord into the camper from the campgorund power post and plug it into the high amp items you use (plug into the normal 15-20 amp household receptical). Simple, no extra wiring, and saves a LOT of money!
I've been doing it this way for several years now. We do a lot of electric griddle or electric skillet cooking and it's done mostly outside. So, it started by running an extension to the campground plug-in and not through the outside plug on the camper. (which almost always popped the breaker inside the camper).
Simple solution, easy to do, and doesn't cost anything.