Ants. You can't keep them out. About twice a year I spray along the edges where the walls meet the floors with Ortho Home Defense Max. I also spray along all the slide seals inside and out. And I give a good coating on the screens below the roof vents. They may get in but they will not live for long.
At the house we have carpenter ants that like the camper and pyramid ants that like to bite us humans. I spread a granular insecticide around the perimeter of the yard and make an extra trip around the camper.