Rick, have you seen this article?
http://garden.org/articles/vie...
This looks really amazingly simple to me, life has gotten in the way of trying it this fall but I'm really planning to build one in the spring!
for smaller hoop tunnels, I think you can zigzag a cord over the top and then open up a side for ventilation and for working/harvesting (the cord holds the covering up).
(cheers from zone 4!)
