I checked back through the thread and I haven't posted this here, so here:
This is what I would do before a HF folder: It steals the construction details from a 1952 Silver Streak Clipper and places it over the Sacred Template. Silver Streak used the simplest possible construction; with a central tube from the hitch, C-channel crossmembers and a carriage bolt pinning the end of the crossmember to the deck. Size the parts and compare the weight. The center tube in the pic looks fat because it was intended to be a fresh water tank.
Instead of a wheelbarrow, I'd look for a 2nd hand car-topper.