Yes it matters where you drill. No problem when you drill through the door, but it is another story iof you want to go through the side. My CO2 tank is on the outside. I just drilled through the metal on the wall and inserted a coat hanger to feel around for cooling lines. When I said drilled through, I mean barely through. You have to watch for the cooling lines that are in there. I noticed a guy made a spacer on his drill bit with wood to keep from goig too deep on youtube. Check it out, has good info on what you are tryig to do. His name was Don Osborn I believe.
Are You Going to Drink all That?