How about your own variation of a Denver observing chair? They fold flat and work fine.
Here are a few links. I used a variant of the last one shown but
I hinged mine at the top rather than the middle but pretty much the same. I also attached an elastic cord at the front underside of the seat and back to keep tension on it at all times.
regards
http://www.tulsawalk.com/projects/de...air/index.html
http://www.schlatter.org/Dad/Astronomy/chair.htm
http://www.umce.ca/astroclubnb/chairjim.htm