By the sounds of it Miles, the fans are a must as I believe that they keep the mould off to a large degree and I think that the drying out is a small price to pay as long as you keep the skin on. Besides, my dog loves chewing the dried bits!
When I bought my chiller, I assumed that any walk in freezer would be good enough and all you needed to do was alter the temperature to 3 deg. This is not actually the case as the compressers are set up a bit different. That said, I believe they can be converted quite cheaply.
As far as drilling through the fridge, this is fine as long as there is nothing in the walls to do with the workings of the fridge. Most small walk in chillers have a self contained compresser/condenser and so no extra workings in the walls or roof (I believe there are some coke fridges that have working in the walls or roof). It is also very advisable to make sure that anything you put through the wall of the fridge is not a good temperature conductor. A metal bolt will take the cold from inside the fridge and lead it outside! If you use plastic rods or something similar then it should be fine.
Cheers
Andy