Decided not to go in the direction of the steel studs due to lack of time before the road trip. Going back to Coroplast fer now.
Here's the revised main belly pan frame...with a majority of the 2x4 wood supports removed and replaced with a top cover of the steel studs. I've also removed the T-nuts that I initially installed into the corner supports and will be going to a standard nut and washer setup for the retaining bolts. I'm guessing the frame weighs about 20lbs or so.
Bottom
Top
I'm gonna use my last full sheet of new black Coroplast fer the major coverage and a roll of aluminum flashing fer the remaining space. I may have to stitch some Coroplast together to protect the aluminum flashing.