first off i would suggest just covering the litter trays with a wet rag tea towels r ideal for this, when you want to bring the crab on to pop give them a good drink of water in a tank or bucket for a few hours make sure its fresh sea water, and keep them out of fridge in a shed or something, this will speed up the popping process, it really isnt worth trying to peel the ones that are not ready as they are not as good bait as the ones that are starting to pop.
I tend to keep 25 to 30 crab in atray and give them agood drink every 3 or 4 days and then move the poppers to a seperate tray and keep them covered with a rag and cool to slow down process ready for the weekend etc
everyone has their own methods but I hope this helps a little mate