I've seen people using white sheer curtains over their beds to allow a little shade and a good amount of air to come through it too. The polyester dries fast in the rain as well.
Target is having a sale on them as we speak which ends tomorrow.
http://www.target.com/c/curtains-win...t_adv_xasd0002
I've seen them setup with a pvc pipe running through each end and set up on a tunnel design.
I've also seen them use shower curtains too.