Hey thanks for all the nice comments!
Funny, my wife wanted me to patent it also. Too much work (and money)! Maybe Progressive will contact me for permission to use
Someone wanted dimensions and build instructions so I've attached a couple of screen shots of the main box that I initially designed in SketchUp. That's really the only part I laid out. The rest of it - the platform and the bar holders - I kind of just did on the fly. A lot of the dimensions were based on wood that I already had so you can certainly make it differently. Plus, I'm not sure if differently rated hitches differ in certain dimensions so that may factor into it as well. Finally, the height of your receiver will dictate other dimensions. Bottom line: I don't promise any of these dimensions will work for you.
The bar "boxes" are 18" long and made up of four pieces at 2 3/8" x 3/4". I think you can probably see how they are assembled but they are in an offset pattern so that it comes out square. I don't really know if there are different size bars so double check that works for you if you are building this. I used pocket holes on each side to attach to the dolly. That might end up being a weak link. That's quite a lever arm on those four screws. I didn't want to glue it down though because I wouldn't have access to the caster nuts if I did.
The four little arms that hold the box to the platform are about 5 1/2" with holes at 4 1/2" on center. Those can be different lengths depending on how much lift you want/need.
The cutouts on the right (as you look down on it) side were done after I had built it all up. I went to test it and realized that after I got the hitch in the receiver and dropped the box down, I couldn't get the dolly out due to the vertical shank sticking down. It took me a few cuts to create an opening to accommodate all the bars and flanges.
It's basically all 3/4" plywood except for the dolly arms for the casters which are just 2x4's.