my method to keep is it fresk, yet dead

If your not particularly sqeamish, you can bring a very sharp but NOT flexible knife, slice the body of the crab open (underside of the abdomen) while the crab is still alive and pull out all the intestines. Crabs spoil ONLY because there are various volatile chemicals within the crab, if you can remove them totally with wither a gloved (or i perfer ungloved hand), the freshness span of the crab will be significantly longer. But remember that putting them into near freezing temperatures is still extremely important

I once went to a Hong Kong fishery and bought a few crabs that you cant buy here, and they just use a heavy knife and slice up all the parts like fish.

You can also eat it raw in that scenario.