I needed a power dolly, I use one 40' RV stall for both my trailers parked nose to tail. If I want to take the back trailer it involved a series of hook-up/pull out/disconnect/hook-up/pull out...... basically a real pain.
My design uses the Pricess Auto ATV winch, the tires
I use are small 8" with 5x4 1/2" bolt pattern that I install on my Boler
when I need to fit it into my garage, (thought multipurposing those would work). Power comes through the trailer wiring harness but I also have built adapters so I can use the vehicle battery
along with a 10/3 extension cord. I installed a momentary rocker switch that does apply the trailer brakes
but the winch provides excellent braking and I have not needed to use it (yet). I used an quick release ball that allows changing between a 1 7/8" and 2" ball
The frame is built from some scrap 3″x4″x 3/8″ thick aluminum angle and some 1.5″x3″x1/8″ aluminum channel and simply bolted together.
More pictures on my Blog
Power direct from trailer plug or adapters to run from TV battery
Quick release interchangable ball mount