I wouldn't mind building one, but everything I've seen always seems to be so bulky in a project box. This is going in my living room/dinning room so it has to look good and compact. At least with a Johnson or Ranco I can either stick it to the back of the unit or try and hide it underneath by the compressor.
If I could build it into the collar that would certainly be my favorite route, I do worry about bit about condensation though. I've been looking for some builds on how people did theirs but I haven't seen much talk on collar installs.