I bought a small refrigerator, put my amp inside it and cut holes in it for the cables. Once the cables are through the fridge, I pack the holes with insulation that gets held in place with tape. You just have to make sure to plug the refrigerator into a power strip that isolates the outlet. And, of course, put some sound dampening material on the outside of the amp fridge so it doesn't mess up your room acoustics, and cones under the fridge and the amp both.
MOST IMPORTANT: Do not set the temp to low. If you do, you run the risk of water in the air condensing and getting in your amp.
MOST IMPORTANT: Do not set the temp to low. If you do, you run the risk of water in the air condensing and getting in your amp.