IMO I would Consider using Rigid Non-Metallic Tubing (PVC) conduit ,boxes,fitting and cover plates. There are other alternatives, but in my past experiance they dont hold up as well to the moisture or condensation. Noloxing all your terminals and connections helps stop corrosion also. Other methods are are approved for these locations ,but I feel this method to work well.
Just my 2 cents.
The PVC sounds like a good idea for some of these.
The ones I have done in the past we try to keep as much outside the cooler box as possible.
Inside depending on job specs I have used RMC, EMT, compression fittings, set screw fittings, LFMC, FMC, WP boxes, normal boxes.
All are NEC compliant IMO.
One important note, always seal the raceway where it passes from inside to outside the cooler. If you do not seal you will very likely have call backs for rotted out devices, fixtures etc. Besides, 300.7(A) requires it.
I agree with bob about his methods, but we all know what devices in these installations look like after time goes on. PVC is cheaper to install ,less time consuming, and as long as it not subjected to physical damage when the temperatures are frigid. it holds up pretty well. Aluminum FS boxes will also work but they seem to fail prematurely.
Since the question is posted in the HazLoc Forum, I am assuming you are storing flammables, not food. Please refer to NFPA 45 (2004) Chpt 12.2.2 and Appendix. Try Google-ing refrigerators and flammables, or other related terms. The internet is full of horrible pictures of refrigerators and freezers and labs that have considerable damage due to improper application of domestic or commercial coolers and freezers. Even if your installation does not fall within the scope of NFPA 45, it contains very good info on flammables and refrigerators or freezers. Expect to spend $$$$.