Stink bugs lay eggs on house plants that have been left outside. When you bring in the plants, the eggs hatch and you have tons of the pests. Have you put a house plant in your camper? If so, that's where they are coming from. They don't "nest" in hidden places like ants etc. but can hatch from the plans over weeks inside. I once saw a hospital that was covered up with the bugs from all the flowers and plants brought in to patients.
House plants need to be treated with insecticide soap in the fall when you bring them inside. That will cut down on the infestations. Of course, they can just be coming in openings, open doors and windows, etc.
We find a Dust-Buster to be the best tool to collect them without enduring the odor.