I was able to get it off with sandblaster using black beauty fine grit for media and 75psi. I did a quick pass with a scraper then hit it with the blaster. Very nasty job, used a full face mask respirator and a bunny suit just in case the undercoating was made up of nasty stuff.

The cheapest and easiest solution that I've found are the 'roto strippers' that you can buy at hardware stores and on eBay.