My top is a little different but has similar issues to yours:
I'm only going to mount one 100W panel so my plan is to make four verticals out of 1 1/2" aluminum angle stock which I'll adhere to the sides of the center ridge with 3m VHB tape. Hopefully I won't have to bolt them to the fiberglass, but I'll check it out before mounting the panels. I have a headliner that makes access to the underside of the fiberglass top a bit of a pain.
Then I'll bolt some aluminum angle crosspieces to them, to which the panels will mount. The panel itself will supply some rigidity and fore-and-aft stability . My panel is 20" wide and the center ridge is a little over a foot wide so there will be some overhang on each side, which shouldn't be an issue. I'm just waiting for the air quality to improve before starting construction.
You could do something similar, mounting the verticals on your sides (you'll probably need more than two sets of verticals and cross pieces), perhaps with the bottom ends of the verticals resting in your gutters to support some of the weight. Given the size of what you need, you'll probably want fore-and-aft rails as well. You could also use a combination of aluminum angle stock and rectangular aluminum tubing.
A bolted together aluminum frame should be adequately strong for your purposes. I don't see any need for welding.