BrewPub, I assume the crabs arrive at your place of business in bushel baskets. Do you have a walk-in cooler (NOT freezer) to store them in? They'd probably do ok in there, with an occasional cold water rinse while in the baskets. You can't partially steam/boil crabs and then finish cookin' them at a late time; yep, you'll get mush!
I know some of the crab carryout places I frequent in the winter have a storage unit/trailer with electric cooling system out back of their place. These businesses are kinda small and have no room for a walk-in cooler inside. This seems to work well for them and might be your best solution. Nuthin' fancy here; you've probably seen these slide-in units in the back of pickup trucks. The carry-outs use them to make the run to the Wholesale Seafood Market in Jessup, stack up the bushel baskets inside, and then when they get back to their place of business, they plug the cooling system into an outside 110V outlet. Good luck.