This time of the year, you shouldn't have much issue as long as you have some fresh water on them. We had 25-30 in my boat last weekend, with just the livewell open to where water could run in and out, and every fish we had was alive. If you move to another spot, just remember to plug or close it off.
As the water warms you can run an aerator and either freeze drink bottles to cool the water, or add small amounts of ice.