Marc, be sure to use the heaviest extension cord available. Better yet, we could make our own 4 gang box to mount to your bench, and use 8 or 10 gauge cable with a plug attached to one end. That way we could also buy and wire in a Saftey (Oh fuck!) shut off switch. The GFCI should be fine. Also, I have a big ass hammerdrill for concrete. I can bring it, along with some Redheads (concrete bolts, easy there Colin) and we can do just that.