There should 'never' be a sewer smell inside your RV.
Make sure water is left in toilet bowl at all times.
Make sure all your pee traps, sinks and shower have water in them, it can evaporate when parked not used in hot weather.
After dumping at a CG fill the tank up with water and dump again to rinse and then add some water to the tank.
I never run with a completely dry black tank. Always have some water in it. If this is a used RV you also may have a build up sewage in the tank from the previous owner not having enough water in it at all times and/or leaving the black tank valve open at CG's where the poop piles up and dries out.
Next time you go to a CG dump and and fill up with water and dump 'several' times and see if that helps.
Your gray tank can smell just like sewer also when it is dirty and nasty. Throw a quart bottle of lemon cleaner down the sink and fill with water and dump. Hope some of the info helps you!