This is the aluminum that from my past experience I suggest to use for any new folding aluminum baidarkas.

I haven't tried it yet. Just looks like a very good idea. In Germany, you'll get this at http://www.wmh.de. The important fact presented here is, there is something better than round tubing, because with the above we can easily attach fasteners to otherwise round tubes.

The 50x20mm and 36x16mm stuff looks promising. It is AlMgSi0.5 which is similar to 6060 quality, the material is used in sailboat masts. Try it sometime.