I would really question whether you will get the rigidity you need out of that set up, but would love to see it work - I’ll look for you at open sauce!
My experience on aluminum step ladders of the well-used variety is that they barely stand up on their own! M4 is not hanging on chains, its actively pulling the corners together. Someone earlier posted that they were having calibration troubles and that when tension was applied that the M4 was ‘floating’. I imagine that was due to the frame flexing into a bowl from the tension.
I would go for a variant of the butterfly/wishbone noted above. And instead of trying to minimize material usage, make 4 identical 4x6 torsion boxes with the corner outriggers and then bolt them together on site. Maybe skinned on both sides with 1/4" plywood so they are light and foam spoil board on top of that. And some access openings to bolt together, but getting it to be flat from there without milling the interfacing parts might be tricky. Basically that hourglass design bisected in both directions. That might exceed the enclosed height of your transport though.
See
https://forums.maslowcnc.com/t/found-some-frame-problems/21409
for notes on larger aluminum rectangle tube flexing…