Looks like a good solid first step. The best way with anything like this is to make one, try it out, make a better one, try it out….repeat, repeat. (cheap gear, they never do this, good gear– they do, but it usually takes a few years). I’m a bivy camper, the old REI Minimalist Bivy. #1 with a Bivy, why no condensation, below about chest level they are just loose fabric that lays on top of your sleeping bag–no air pocket, no condensation [every kid on Kickstarter with a bivy-hammock-flying car seems to be designing condensation bags instead of whatever it is they’re claiming/wishing].
The mesh seems a bit too low, but that might be nice in hot weather. I like the idea of the rain fly– it gets wet it’s on the outside and can dry out during the day. My bivy came with a warning to always leave it partially unzipped to breath. In my living room it’s stifling– but outdoors, by itself, inside my tent or rain fly? That has never ever been an issue.
My procedure: Usually I just let the air out of my mattress in the morning and then just loosely roll up the bivy, inside is my sleeping bag, liner, air mattress. Then I just tie it to my back pack. It gets some airing out. In camp, I roll it out, blow up my mattress and I’m ready for bed. If it’s not raining I’d rather sleep in the bivy than the tent– I can see more, hear more. Even when I’m looking at an overcast moonless night, I’m not looking at the same silnylon tent inside–that view never changes.
Rain. My bivy has no fly. My first night at 10,000 feet outside the hut on Kitadake, in Japan, blowing wind and rain. The solution was obvious–I just turned the bivy sideways away from the rain. Kept almost all of it out. So the rain ‘bathtub’ should run up both sides to allow for this. A rain flap like yours will have four positions. 1. not needed. rolled up. 2. Very cold, pulled up all the way with a small hole 3. Rain mostly from the left–fly pulled up, bivy rotated to the right and a slight opening on the right side. 4. Rain from the right– just the opposite. (and rain from above your head? turn around or cover up like #2)
I modified my Minimalist by adding a couple of grosgrain loops to the mesh. Otherwise the mesh lays on my face–mosquitoes have no problems with this. I usually stake a hiking pole or two, stake a string across and to stakes on either side and then lift up the mesh at the loops.
Another thing I find I do. I like to pack(rat) a lot of small stuff inside the top of the bivy. My iPhone, glasses, water bottle, bear spray, book, journal…. So extra ‘pockets’? up there is handy. (But ask others, I might just be a weirdo).
Also when I sleep in my bivy under my rainfly and the ground isn’t level, my bivy and me slide downhill. So maybe a couple of grosgrain loops at the top corners, so if you do need to run some line to a stake you can do it.
I don’t fully understand how you’re going to close any gaps between the mesh, dew/fly and bag. One thing about mosquitoes is: they always find the hole because more air is moving through a hole than through the mesh.
And the best thing about a bivy is they’re lightweight and roll up small. Some bivys weigh almost as much as tents… I have a nice camping hammock, but all the stuff weighs almost as much as my Big Agnes tent, and the tent doesn’t need trees to work. Hope this helps.
