I ordered 3 of them from a guy in MB he sent them to me on the bus. Funny enough I was just looking at a old document I had for tubs and all the parts costs. IF I can find it and details I will let you know. Tubs are very strong, centrifical molding which was suppose to be stronger. I originally made a T frame for axles and hitch for my first box , then when got these tubs I pulled old box off and added a 1" square tubing same as bottom to bolt to .
Found it, here is teh web site where I got them http://goodoutdoors.theshoppe.com/4_trailer_tub.html Looks like they moved to the east coast and wanting to get out of it, maybe not building them any longer, but you can try. These guys are an option too http://schtrailers.com/PlasticTub.html