I agree with what Garry said above, however, I think the bulb seal on my trailer contacts another lip at the bottom half when the top is down. In any case, since I've owned the trailer (bought it in 2007), I've never found any particular evidence of bugs inside through year after year of storage when we weren't using it.
I DID have mice in it, inside the cabinet in the bathroom and in a cabinet beside the refrigerator (that had an adjoining pathway to the bathroom behind or under the fridge), but I mouseproofed the trailer with hardware cloth (a wire screen) and pestblock expanding foam and have had no further visitors.
Hi-Lo 1707T - Tire Minder TPMS on Tow Vehicle and Trailer, 300W Solar Battery Charger, Equal-i-zer WDH
2014 F150 Platinum 4x4 3.5L EcoBoost SCrew