I have an upcoming Colorado thru-hike that I'm planning gear for, and one of the issues is whether or not to get a bivy for my quilt for use under a poncho tarp. So the ideas here are specific to this purpose.

In my case, the primary functions of the bivy would be:
1) groundcloth
2) draft protection for windy nights
3) protection from blown rain under a somewhat scant (5'4'' wide) poncho tarp
4) (possibly) bug protection

What is NOT necessarily needed is additional warmth (I will have a really warm down quilt)

I've been looking at commercial bivy options and nothing really seems to be a perfectly optimal solution, especially considering the cost ($140 and up) for a bivy to my specifications. They generally make it harder to get up to pee in the night and limit your ventilation options.

So here's what I'm thinking of doing. Cut an double Adventure Medical emergency blanket to size and duct-tape the corners to create a bathtub style floor that would be high enough to block ground-level drafts from creeping under the quilt. Then equip the corners -- if necessary (I'll have to see) -- with tie-outs that can be tied to the poncho tarp above, probably via elastic cord. I think this would adequately perform the first 3 functions, and for the 4th (bug protection) I would wear a headnet of some kind to sleep when necessary (often not necessary after dusk, as I understand). This would give me the freedom to sit up, ventilate as necessary, get up at night, and generally not be at all constricted by the bivy. And it would weigh under 4 oz total including the headnet.

Has anyone tried anything similar? Are their problems with this idea that I have overlooked?

i was thinking a few months ago of just folding up 'wings' on my tyvek to seal off the drafts, maybe some loose elastic holding them up/together. i don't know if you use your space blanket as ground sheet, if not this would save you an item

Yes, I do. I have been thinking about the design I proposed above and think that it is probably too complicated, and the bathtub corners might fall down or get crushed too easily. In addition, I would lose the functionality of the space blanket itself, which can provide extra rain coverage in case of severe rain.

So, what I've thought of is this. I can put 4 tie-outs on the corners of the 2-person space blanket without trimming it, and sleep on it _diagonally_ rather than parallel. I would then pull those corners upwards and tie them to the shelter above. Basically the same effect, with better additional rain protection.

Have fun.

Edited by guesting on 06/12/2008 18:59:00 MDT.