I've already built an aluminum kayak. It's a greenland style boat out of 5052 14ga which is about 0.08". It's 17'4" x 21.5" and weighs in at 55lbs. It is rock solid. I had it in between 2 saw horses (6 feet apart) and sat in the cockpit. The kayak didn't flex at all. I'm going build some more but they will be out of 16ga which is about 0.06" and they should weigh in around 45 to 50lbs. I plan on putting a 0.25"round rod backing in all the seams. This will help reinforce the seam (since the welds will be ground out) and help dissipate some of the heat. I have been welding alumium as thin as 0.03" for a long time. The best way to weld aluminum this thin is TIG. I started out trying to MIG it for speed, but that turned out to be a mess. I'm planing on producing these boats so any feed back would be great. I'm in the prototype stage and I'm trying to deal with the corrosion issue.