I know this has been done before, and the other threads were a great help to me, but I just wanted to share my experience.
I started with a Frigidaire 4.4 Cu. Ft. Compact Refrigerator (model: FRC445GM).
I took the top off and dug out the foam where I wanted to drill. The top comes off pretty easy, but you do have to be careful not to break the top while pulling it off. The coolant lines run about 1.5" apart.
I wanted to reinforce the top so the tower would be screwed down firmly. So, I cut a .5" sheet of plywood to 13"x16" and dug out the foam where it was going to sit.
Here is a picture of a dry run with the copper pipes sticking up and the top on to make sure everything lined up and fit.
I filled the hole that I cut out with some foam and glued the wood to the top of the refrigerator. Also right before I put everything together I placed some foam between the wood and existing foam since I didn't cut it flat originally. While everything was drying I put a full keg on top and today everything was secured very well and the top fells very solid.
Here is the finished product: