You alluded to the problem I have about once a season in your last line:

"unless I sit or lay in such a way that a gap opens"

When I do this on a thick mosquito day the bugs will create a "bracelet" of bites around that small exposed area.

I recently bought a set of Dirty Girl gators to see if they will solve the problem. I don't like the fuss of gators, however. That's why I was considering the goretex socks.