We found this one at Tech Central Racing in Bonita Springs, Florida in December 2022. The structural parts are all aluminum extrusions with T-slots, then assembled with a few basic brackets and lots of T-head bolts.

They say it doesn't weigh much and tows easily. I don't know if all the brackets and bolts are more efficient that welding, but it seems to work. Maybe it was a kit shipped disassembled in a more compact package for the buyer to assemble after delivery. Or possibly some different configurations of width and length might be assembled from similar components (like an Erector Set). I may have the opportunity to pursue more questions later, like who made it, and is it still available.