Agree with Papa. If possible don't keep them onboard or in the tow vehicle. If you MUST leave it in the tow vehicle, keep receipts from day 1 purchases (bait, food, hotel etc) so you can reasonably prove you fished two days.
Some of the fisherman friendly lodging locations have both cleaning tables and freezer space available for guys to use. Leave it where ya lodge and swing back there to pick up after day 2.
Also...some cleaners can keep it refrigerated overnight for late day 2 pickup.