i would suggest that you think of this or any kind of bivy
as just one layer in a shelter..after sleeping under a canoe
with a tarp over it for a few trips i could see i needed
something bug and mouse proof..i got a tiny tent that was
more of a bivy and used it under the boat and tarp and
got got total shelter..in a longer term sitution your $19
bivy would just be the inside layer of some sort of plastic
and brush shelter..