I had one that was camping above my horizontal propane tank and occasionally found evidence on top of my slide out generator. I didn't beleive in them, but I tried one of the ultrasonic devices. My motor home is parked between a wall and my house. The wall, about mid coach has the outlet that powers the coach. I plugged the ultrasonic deivce in so that it was pointed toward the coach, about two feet away and in the middle of the coach. I haven't had issues since. I do know if it's coincidence or not.
Don & Mary
2014 Newmar Dutch Star - All Electric - 450 ISL
2016 GMC Canyon 4WD Crew Cab