http://www.4wd.com/productdetails.as...4&partID=10626
For the aftermarket galvanized frame at $2350

Considering that the aftermarket frames are mandrel bent in both
directions (read LARGE setup cost for the first one!), you would need to
cut and weld the aluminum frame. IIRC there are 6 bends per side so 6
cut and weld joints in aluminum. Assuming you use something like
6061-T6, the weld areas will eventually age harden to about 6061-T4. To
get a reasonable compromise between cost and strength and stiffness, you
would need to go to a 2"x5" or 3"x5" aluminum rail. Other posters have
mentioned the fatigue issues, I think I'd be more worried about weld
strength, HAZ areas, and the lower yield strength near the welds. THEN
you get to worry about fatigue.

The frame dimensions are commonly available, it's just a matter of
deciding on cut and weld vs mandrel bent.

mark wrote:
I would liketo build a new frame for my jeep CJ-7 and want something
that will not rust, ever. Would 2" X 4" X 1/4" wall aluminum tubing be
strong enough. How would that compare in strength to 2" X 4" X 1/8"
wall steel which is what aftermarket frames are made from?