The dollies work great on a concrete floor.
Each dolly has three 4" steel swivel casters. I am thinking about making two of the dollies have a least one stationary wheel (just thinking though). It is real nice to be able to move the TC sideways.
Each dolly is made of 2 pieces of 3/4" x 2' x2' treated plywood, glued and held together by the 12 carriage bolts that attach the casters.
Most likely will incorporate those 4 dollies into a 5' x 8' dolly to move the TC with. There is too much stress on the front jacks when using the individual dollies.