Hi,
I'm not sure if we're talking the same thing here, but I recently purchased an EdgeStar BR200BL and added a dual tap to it. The tower that comes with the EdgeStar (if you order the full kit) actually mounts by inserting tabs into the kegerator and turning the tower to lock it in place. The tower I ordered had the normal flange with four bolts, so I had to drill the bolt holes into mine.
The tower had a rubber gasket, which I used as a template to line up the tower and locate the holes. I put masking tape on the top of the kegerator to prevent scratching and so I could mark the hole location. Drilling was easy. Once I drilled through the first layer of plastic, I hit foam insulation and then the plastic lining the inside of the kegerator. I assume most kegerators are built the same way.
I needed 1/4" holes for the bolts, so I used a 1/8" first and then followed up with the 1/4". I don't know if that was necessary, but I hate to start out with a large bit. You do need to take a little care to keep the drill bit straight up and down. Once you're through the first layer of plastic, the foam insulation doesn't provide any resistance, so you want to make sure you don't let the drill tilt before you drill through the second layer of plastic. My kegerator actually came with two shelves, so I put one in the highest position and set a box lid inside while I was drilling to catch the plastic and foam that dropped through.
Everything went well on mine, other than the fact that the bolts that came with the tower turned out to be 1/4" too short when I got done. I wanted to stay with stainless steel, so I ended up having to order the ones I needed from the Home Depot website. The shipping was more than the bolts, but I couldn't find stainless steel at any of our hardware stores.
I hope this helps!