This works for carribean reef roaches. No reason it wouldn't work farther north on the over grown mudbugs found up there.
The primary considerations in keeping any crustacean alive is to keep the gills wet and well airated and keep the critter at or near the temperature they were in before harvest.
The method used farther south is to wrap the catch bag in a towell soaked in sea water. This is then kept in the shade/air conditioning to maintain a temp of near 70°-80°F. This will allow fresh air to get to the gills while maintaining a 100% humidity level. if the towell starts to dry out dump more sea water on it. This method will keep reef roaches alive for up to 3 days. Farther north this may require an ice pack/chest to keep the temperature constant.
As far as cooking shellfish the key to boiling is to match the natural salt content in the meat to the salt content in the boiling water. More salt in the water than the meat makes the meat loose water, and thus get tougher, but it also makes it shrink a bit and easier to separate the meat from the shell. If the water has less salt than the meat the meat will gain water, thus causing the meat to swell. The meat will be tender, but a real bear to separate from the smaller sections of the shell. The best bet is an exact salt osmodic pressure match, or to be more exact the water you took them out of in the first place. The meat will neither gain nor loose water. It will still be tender and still easy to peel. Please note that the osmodic pressure involves both the major and minor salts. It's really hard to match the minor salts unless you bring the water home with you. This is the one advantage divers have over the supermarket crowd. We can get the right water! Without the right water steaming is the next best thing, but it's a poor second at best.
If doing a cajun style boil simply start the "tea" with the seawater by adding the ground pepper, citrus, onions, carrots, and fresh garlic, but NO SALT! Reef roaches respond well to cajun spices, I expect your monster mudbugs will too.
FT