Thanks. I've got the same problem I've seen discussed elsewhere on the forum, but I can't keep a floating live box. When I check my pots on my way home from work, I may have a 2-4 crabs. I want to keep them 'til the week end when I can either steam and eat 'em or steam and freeze them. So I'm talking about keeping up to a dozen crabs for about 5-7 days.
At some point the sport of crabbing can be overcome by the cost. It may be more reasonable to buy crabs then to build a livewell system for 2 - 4 crabs a day. You need bay or river water preferred and a pump/ filter system unless it will be at the pier and you still need a pump 24/7.