Fermwrap heater, a little foam insulation to separate from lagering - sounds good. Don't know, haven't tried it. All I make are ales, and mine go from secondary into the kegs (kegerator) no lagering. Perhaps someone else will chime in....?
I liked my collar/kegerator until I began seeing the handiwork of some of the others here...now mine seems 'functional'
However, in the DIY forum, under the 'sticky's - there are hours of threads to look thru for ideas. Some collars sit on the base, others are mounted to the lid. Some are covered in brick and tile, with the taps on all kinds of towers. Some folks have 12 perlicks going, with a plaid paint scheme on the way.
The basics for the collar are 2x4 on edge, frame the top or base. When attached to the base, sometimes faced out with a 1x6 to hang around the edge. Paint or stain, silicone to the top or bottom. The whole idea of a collar is twofold: to give you more height inside the freezer - utilizing the compressor hump - and to give you something to mount the shanks and taps to. You certainly don't want to drill thru the wall of the freezer - the freon lines wrap around under the skin.