I built a custom Mini trailer when I restored/rebuilt the 1980 Mini 1000 and installed a 1380 with 2.95:1 FD. All up weight of loaded sedan & trailer ready to travel is approx. 2,500 pounds/trailer contributing about 20% of that weight.
No issues towing...don't know the trailer is there. Hauling at 70 mph uphill down dale not a problem. Combo can easily fit in a standard parking stall and is an easy back out if one is careful.
The hitch is designed to bolt through the rear subbie crossmember (mild steel) with 1/4 inch angle iron to reinforce, with the hitch reach (torque control) to be bolted into the rear seat pan. Side exit exhaust.
Very much like many Mini trailers but built from 2 rear ends mated through the rear wheel arches, with domed/guttered roof made from 6 pieces out of 2 Mini roofs. Boxed sub frame with single leaf springs, stainless steel dead axle with Mini hubs - axle has flanges ala trailing arms with welded backing plates, Mini rear axles and bearing mount so have 4 rear hubs on the road with trailer tracking as per Cooper S suspension on the sedan .
You can see photos of the trailer build at www.miniman.ca.
I towed this trailer to Arizona, across the states to Maryland and back 8,500 miles on its maiden voyage, later to California, Minnesota among other trips.