I was wondering if you would get the legs aligned correctly, but I see they aren't attached yet.
I tend to build mine in situ. I have a wobbly unistrut set of legs I bent (in conduit bender) and bolted to my old rack. It has X and Y diagonals, which do get in the way, and it is awkward to remove one-man. (fits in rear 4 pockets of pickup bed. Balance of rack is bolted through cab roof and supported from front bumper.)
Yours will be more presentable than mine, but also heavier. Yours is for panels, mine for random cargo, about 16' full length of pickup.
Looks like you could have a little cargo space. Center would be more difficult to load. How about mounting panels to one side, and make a tilt-up (to avoid shading when not in use) vertical, leaving about 10" or so for stacking lumber or pipe? You could load from side of vehicle.
Are you able to hoist it to the ceiling and drive under to install?