Thanks for all for the leads. Lots of information in those places. I am looking to make a vestibule for a bivy/tent cross (Northstar Bivy) I picked up from Cabela's in the early 90s. It is lightweight and I have 3 of them, if I can rig up a vestibule for wet weather hunkering, it will work great for my desired re-entry into backpacking soon.