I've been thinking about the same type of set up, only using some PVC fittings, a nylon tarp and some bungie cord/straps. I would use 4 1.5in PVC T's
(note: outside diameter of NRS unbendable pipe is 1 5/8in) with the upright reduced to 1in
mounted to the frame (and hoseclamped using the above mentioned piece). Then add uprights of 1in sch 40 pvc and 1in side inlet 90's
to make a square roof. I would glue some connections and use some tab lock pins
in order to make it set up/down friendly (where it meets the T's and some on the square roof so that it breaks into about 8 sections). Then use a standard sized tarp over the top with cams or bungies holding it in place.
I have seen this used, but have not built one yet. As I do more desert runs, it seems that this setup would give better coverage and with a nice stuff sack could be set and torn down and stored quite easily.
If anyone has a better way to make this please let me know.