pic: Sheet Metal Drivetrain

[DonRotolo]

There is another strengthening method used for sheet metal, and that is beading. Basically you put a 3/8" wide x 1/8" deep (can be larger or smaller) "bump" along the length of a straight member. This adds significant rigidity to the part; however it complicates the flat geometry (what needs to be fabricated/cut when the metal is still flat).

Here is one type; they also make beading dies for presses that are better for beading like you'd need for such a chassis.

Nice CAD work; The 0.090 material would be plenty think. With some creativity, you might be able to go down a gauge or two. One thing to consider is the long unsupported members: These tend to be very weak in compression (they fold) and, unless you are certain they are only in tension, you need to avoid making them a "slender column". This is where flanges and beading and other deformations will help most.