When I sealed the power cord inlet and spray foamed all the pipe entrances (underneath floor and under sinks) on our very remote vacation TT, we finally kept them away. And, like you, we got a few in the motorhome while in a metal building. We did a hospital grade cleaning to remove the scent trails (hopefully), and caulked every opening, and made the power cord entrance a twist on style, so that no bay door, or little plastic cover could be pushed open. Does that kitty litter idea work? I've got to remember that one, too!