“Bugs come in a massive array of sizes and shapes, if they want in and are determined enough they’ll get in”
Like J Scott and others, this hasn’t been my experience. With mosquitoes. possibly because of using mosquito coils, the most effective for me being the PIC. But would not actually put one IN the tent like Chris Townsend (‘Walking the Yukon’, ‘The Advanced Backpacker’), who once posted on BPL that he burns them right inside the tent. Guess things get extremely buggy up in the Yukon, but not a good idea to inhale them in a confined area, and once in the tent for the night, you can let the coil,or piece of coil, burn out, as the tent does keep the bugs out. Have not found them active during the wee hours when leaving the tent for a few minutes. Maybe they need a few minutes to get into attack formation, or maybe because the locales, CO and northern New England, get chilly during the nights, even in the summer, or maybe because of camping at higher altitudes, not near marshy breeding grounds. Granted, this could change with climate warming. Do mosquitoes ever sleep?
With creepy crawlers, same answer. They don’t get in unless hitching a ride. So maybe your shelter needs buttoning up if it is going to provide insect protection. Realize a great many packers, especially on BPL, use tarps with less than full double walls and floors. Those shelters can’t be fully buttoned up.
Yes, full double walls, solid or netting, are probably going to be a bit heavier; but with fabrics and netting now 1/2 to 1 oz/sq/yd, ranging from DCF to silnylon to bomber netting, total wall weight can approach 1.5 osy, which was unheard of just a few years ago. So the weight penalties of full double wall are no longer so stark.
I remember driving up to Maine a few Junes ago, and parking near an AT crossing in the 100 mile wilderness not far from Katahdin to hike in to Rainbow Lake, which has beautiful camping on the West shore, a good distance from the AT. All the hikers near where I parked were wearing headnets, and sitting near the trail junction looking very miserable, as the skeeters were at the height of their annual swarm. Not the best choice of time to hike, but once I got into the woods, saw no one, and Ben’s DEET was enough to keep the buggers away.
Granted, there was a July trip to the Big Horns in WY many summers ago, where the skeeters were the worst I’ve seen. Could have been a nice loop trip, but after a couple days, got the heck out of there. Lots of boy scouts and horsepackers. One thing skeeters and bears have in common, they are attracted to people, and the more people, the more attraction. It’s the food, of course. A few skeeters did get into the tent on entry, but they were defenseless once captured inside the netting, and easily squashed.
But I usually avoid the swarm season, regarding hiking as a fun, not a masochistic activity. Realize for end-to-enders, that is not an option; but there are still flip-flopping and other schemes to get around swarm seasons and post-holing in deep snow. Except maybe for Chris in Arctic.