in order to build a custom fit insulation for the cavities i've built some hot wire foam cutting machines to cut the 2" thick polyurethane thermal insulation. The wire i use is a .010 piano wire typically used for suspensions (thats what we had i the lab). Nominal current is about 1.5A at a couple of volts, so any simple power supply does the job.

Here are some pictures of the large foam cutter to cut the 48" x 48" boards into smaller peaces and the circle cutting device:

original panel size

pre-cut parts:

cutting into smaller segments:

surface comparison before and after hot wire cutting:

circle cutter:

some cut parts:

ready to cut the rest...