We do mobile workshops using bike trailers. We haul two ez-up canopies, two folding tables, three big tool boxes (two with drawers), a paper file box, a kitty litter tub with lubes and solvents, three or four folding repair stands, a truing stand, two pumps, a sandwich board sign, banner, and three 18 gal tubs full of stuff . This requires two medium Bikes At Work trailers. If you want to haul bikes, too, you'll need to make do with not much stuff and two trailers or three trailers. Keep in mind each trailer needs a person to pull it... maybe not so hard to come by in Minneapolis during the summer.

I have not used the Surly trailers. The hitch system does appear stronger than the Bikes At Work one. However, I like that the Bikes At Work trailers are mostly aluminum as opposed to the Surly's chromoly; the BAW seems to have more tie down spots, and the side rails on the BAW seem helpful for keeping stuff on board.

Here's a short video of me and some jerk pulling the two trailers. Forgive the Queen: http://vimeo.com/62093021

-Paul
The Bicycle Tree
P.O. Box 11293
Santa Ana, CA 92711
http://www.thebicycletree.org
info@thebicycletree.org