Here in Maryland, they have been a big nuisance. They infested my TT last fall when they needed a place to winter-over. They gain entry mainly thru the heater exhaust vent, open windows (even with the screens closed), open slide outs, roof top air conditioners, and refrigerator side panels. I now seal the heater exhaust vent, close the windows, close the slide out during Sept & early Oct, cover the air conditioner and tape where the cover did not seal completely, and remove the outside fridge cover - then place a sheet of aluminum foil over the opening and replace the cover. Of course this is with the TT in the driveway - not camping. It's a pain, but it's worth it. Currently our house and camper are plastered wth these bugs when the temp is above 60 degrees F, but I've been able to keep them out of the TT by taking these steps.
2010 Surveyor 294
2006 Ford E-350 Van 5.4