Wow, been travelling for a while & haven't been able to reply. Now that Leinbach one looks pretty nice, in particular the triangular rack that would stiffen the lower platform support considerably. But I already have the TSC version, which is made mostly from 3 x 3 x 1/4" angle.
Studor's is the closest to what I was considering. And I figure the solid sides would gve me the ability to haul other bulk stuff like leaves, grass clippings, etc. - which led to my next thought - why not hinge it in the back and make it "dumpable"? a safety chain could keep it from going too far. I'm moving to final design stages now, if I can get one of the fab shops we work with to weld up a hinge plate for the bottom, I'm good to go.
But in typical "engineer" fashion (hopeless dweeb, as my kids say), I measured the frame up and threw it into the idiot box (computer) and sure enough: TSC changed the position of the lower hitch pin holes so that they can use the same piece for both sides - both holes are 15.5" from the end of the vertical 3 x 3 angle. Which means I'll probably have to get the shop to drill another hole for where I want my pins to go...
Thanks all,
Tom