Usually there is a limit imposed on the campsites. That can be from 6-8 depending on the park. Most parks will make exceptions but may charge an extra fee for the extra person(s). That said, it's entirely up to the park...their park, their rules. Simple answer is find another park. I understand why the rules in place, think spring break, but most parks have leeway in it's enforcement. I'd rather have a FAMILY of 7 or 8 camped next to me than a rowdy bunch of drunks numbering 6.....best of luck...
BTW, that 30' camper is going to feel like a 10' camper real quickly...Dennis