Get out the Popcorn. Here comes the age old fight over Chemicals Versus water........ lol
On a serious note though, If the camper you purchased has a clogged, or broken Vent pipe, it is possible that is you issue. I had that (Clogged) in an older trailer once and had a friend buy a new one that had the Vent pipe separate because it wasn't glued together at the joint.
Those are just 2 things I would start with if it were me. Simple to check for. Of course it could be a whole Gambit of other things, and not even related to my suggestions. lol
(and for the Record I use Chemicals AND a TON of water so I don't have an opinion on that) :)