I thought about doing it to my 33 when I did it. I didn't research it much, but was thinking of putting plastic on the cabinet and liner. After that full the void with foam and once dry remove the liner and have a molded piece of insulation.
Appliances use spray stuff now. And it seems to work well. Something else that I have wondered is why my refrigerator runs silently and my soda machines are louder. Seems like we could make them run quieter.
The plastic wrap with the spray in is an interesting idea. What would work great is that stuff that is stuck on the front of TV screens and other metal parts in packing to avoid scratching. I think with the appliances there is no problem using the spray in because there is no expectation to ever pull them apart. Life expectancy on most appliances is about 7 years--not like the old days. I still think that foam board would be a better alternative to regular insulation than the spray in. Easier to sculpt and no mess if you have to take it apart down the road.
On the noise difference, I know my refrigerator is up against the wall between two cabinets so the sound if any would be more muffled. It also has the vented cardboard backed with insulation covering the back of the compressor opening. My USS 64 is not that loud but I think I could quiet it down by replacing all of the fans and putting some rubber bushings on the compressor mounts. On most soda machines the compressor opening in the back is wide open so perhaps covering that with a vented piece of cardboard backed with insulation would dampen the sound a lot more. Not sure what that would do to the ventilation of the compressor area though. The only noise I hear out of mine is when the compressor cycles and it rattles a bit. That is an interesting question on the difference in noise levels though.
Tim