Haven't seen any plans to speak of- but the nice thing is about 80/20 is its so versitle. Sorta a grown-up erector set. They have some free software/catalog for "messing with" and sorting out the materials available. If you look in the member's gallerys - System2 is an 80/20 and plastics. No torsion box but you could do one.
I made the System1 and then System2 using 15x30 sections. System1 wasn't large enough - or stable enough to meet my needs. System2 is very close to the dimensions you mention.
:cheers: Jim
Experience is the BEST Teacher. Is that why it usually arrives in a shower of sparks, flash of light, loud bang, a cloud of smoke, AND -- a BILL to pay? You usually get it -- just after you need it.