I recall reading a post here a while back.
The person complained about bugs & Mosquitoes was coming into their trailer and had suggested they were not sure how they were getting in.
Now, before I say my bit maybe someone has already mentioned the fix. If not here's what I found with our TT.
I just recently fixed a leak on the hot water heater and as I was removing/replacing the propane line to the water heater I noticed quite a large port where the propane line fed through to the burner.
Hmmm. I had lots of leftover butyl tape on a roll. I cut off about 4 or 5 inches and fitted the tape around the hole. Butyl as we know will flex and you can virtually shape it to your needs.. It took me about 2 minutes and now that hole is sealed (with respect to insects) .
You might also want to check the ports where the inlet or outlet holes are for you other pipes and drains. If insects want in, they'll get in.
ALSO: when I completed the water heater installation I noticed a crack down where the front wall of the TT meets the floor. It looks like there was a tin overlap between wall and floor, more so used to complete any unsealed areas. I filled the crack with regular household acrylic caulking in a tube. I purposely put lots in there because we don't see it as it's hidden from eyes. Then I installed an "L" bracket and with long 1/4 inch carriage bolts I tighten and drew the wall towards to floor. Then I caulked under the TT to seal the other side. Face it, it's a 1985 and no matter its condition we will find fatigue here and there. Nature of the beast and the best any of us could do is to be on top of things, as best we can.
We're taking off for a longer trip tomorrow and lots of miles. I checked the wheel bearings and bearing races for condition and re-greased with bearing grease
Hope this helps someone
Jerry & Debbie
Ford Explorer 4.6 Triton V8, AWD, 4x4
1985 Sunline Saturn T-1350
Ham radio VE3JCJ, VHF, UHF and HF