Hey I work in the trailer industry as a design Engineer and I can tell you there is a lot easier way to do this than a hand truck. unless you are going to be testing 30 to 40 trailers a day you can build one like the ones Croft trailer supplies make in a tool box and use a break a way battary to run the entire thing. Here is a link to see what Crofts box look like http://www.crofttrailer.com/site/pro...1/details.html
we use this type of box on almost every trailer we make. this system is set up with a in line fuse for each companant you will test. they are cheaper than the circut breakers if you are only going to be using it every once in a while. they mount a 4 way, 6 way and a 7 way plug in the end of thiers with a ground plate on the backside of them. I hope this helps. If you would like me to go into greater details I can just buzz me on here and let me know!
Big Tex Trailers