PVC pipe: 1.4oz per foot
4 ft minimum, 6 for rectangular frame, plus couplings.
Aluminum bar, 1/2"x1/8": 1.75oz per foot
4 ft. total
Screen door framing: .75 oz per foot.
4 ft. total, plus something to cover the ends.
Seems like the aluminum would way much more than the pvc, but I guess not.
PVC: If I needed a square frame, it would be easy to construct with 90 degree ells. Can also take a hit and rebound, to a point.
Aluminum: Malleable and can be reformed and adjusted.
Screen frame: Lightest, but would be permanently kinked if it took a hit, and is only flexible up to a point. Ends would be sharp.
I think I'll try the pvc first. I could feed it through the lashing loops on the back of the pack, and the sleeping pad should keep the lumps away from my back.