>Could you also think about just using DEET instead of the head net?
I'd really advise against this on a thru-hike. There are going to be at least a couple of weeks out there where the mosquitoes will be fairly overwhelming, and times when the flying pests are gnats and other things that aren't affected by DEET. He could maybe get by with a head net, but he already said he felt claustrophobic in a TG bivy with the head netting sewn on.
Another possibility might be one of the oware double bivies. With your situation, though, I think it's tough to beat a tarptent for being spacious and bug-free.