Boat: CS36Merlin, "La Belle Aurore" Ben393 "Breathless"
On my CS36 Merlin I put a clear plexiglas divider in with some holes in it. This had the effect of making a "freezer" section (the section with the holding plate in it) and a "fridge" section, the rest of the box.
I would increase insulation at more than the bottom but even that will help a bit. Gluing in insulating foam, then covering that with plastic panels and caulking all seams and corners is the quickest and easiest.
Chesapeake Bay, ICW Hampton Roads To Key West, The Gulf Coast, The Bahamas
As others indicate, insulation is the key to refer' efficiency: top, sides, then bottom (in order of efficacy).
A flexible insulated blanket, that conforms to the ever-reducing top of your stored perishables, works better than a fixed "brick" to reduce displacement (as you consume stores).
Gord May "If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
i forgot to mention that another issue is that i would really like to reduce the depth of the box. it sounds like i could use a lot of closed cell foam on the bottom and some on the sides. probably good to leave some way for any fluids to get to the drain also.
sometimes the things that may or may not be true are the things a man needs to believe in the most.