Update: The basement freezer is now 20 tiles long with cooler at the top & muffler at the bottom. It reliably cools the top to -5’C, which is enough to freeze tainted fat. Both cold and hot air seem to have a ~10 tile limit, so they only briefly touch in the middle of the vehicle.
Now I effectively have a 4000L freezer (4 tiles at -5’C). 53 minifreezers at a cost of just 120W of power.
The effect of vehicle coolers does not stack.