They do make covers for the AC unit. ADCO makes them. I have one I use in the off season. I did spray it when new with 303UV protectant which helps it live longer. The sun really does a job on these types of covers
So yes, do use a cover in the off season. It keeps the weather out of the AC unit as well.
Now to the wasps. Yes, every now and then a wasp next shows up in the roof unit above the camper. It has not been a major problem for me.
See this post. It shows the inside of the upper unit. And you can see the small wasp nests I found when I pulled the cover. They where dead, but still there. In our area we seem to have more issues with the wasp nests in the shore power box when I go to plug in. Always lift the shore power lid cover slow and be on guard.
The upper unit is sealed up pretty good from the inside. Adult size wasps are not going to fly in unless the gasket on the cover over the evaporator coil is shot and the cover buckled. That being said, nature does find a way to survive. It is not beyond impossible that eggs may have been laid inside the camper and maybe in the AC area. They then are born inside and become active.
Thinking on this, what year/model camper do you have? The 2003 and older models use to have a stove fan range hood vent to the outside. if that vent cover never closed tight it might allow insects to come in through the fan vent.
Hope this helps.
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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