I made one out of dri duck ponchos for my Expedition. It wasn't that hard.
After I sewed the ponchos together to give me the length,,, I started pinning, and cutting till I had it wrapped the way I wanted. This one doesnt have a bottom opening, since I had the zipper mod already on the HH.
I have this one and a HH SS, and don't use either one. I think they are over rated and to much hassle in my opinion.