I've found, after being a kegerator owner and builder for 15+ years, that reigning in your expectations of foam is the best way to fix foamy beer. Basically, you can build a cheap tower cooler, or buy one off ebay and that will help tremendously, and lengthening your lines for decreased pressure at the tap are your only two options that will work for certain. Both are quite easy. A length of 1" copper pipe holds my beer lines, extends a few inches into the fridge/freezer section, where a copper T connects to the OUT of my tower cooler, and the other is open and the beer lines flow into it. The copper gets very cold, and holds the beer in the tower at lower temps.
Anway, I'm rambling, but I've spent far too many hours of my life working on my kegerator.
The biggest risk to putting a tower on a chest freezer (other then the risk of the lid falling on your head when you're working in it) is that you'll forget to pull the keezer-ator away from the wall before you lift your lid and your tower will damage the wall, or the wall will damage your tower, or both. Being mindful is key. Casters would help too fwiw, because then pulling it away from the wall would be pretty easy.