All this talk about dipping/blasting...., What to do if you can't afford either? Options

[bondo]

I'm on a serious budget here, and I'm in the process of removing paint/seam sealer/rust. I've got most things under control, but what's the best way to get that nasty rust harboring foam out of the corners of the rear fenders? Also, where else did they put that junk? Aslo, what's the best way to remove undercoating?

[bondo]

Of all these, I can only see the heat gun doing anything to the foam, and even then probably not much. Should i just go with my instinct and burn it out with a torch? (I'm talking about the stuff that's crammed into the most inaccessable places, like above the taillights, and above the cutouts for the door handles) I would really like to know where else this stuff is so I can get it before it gets me (IMG:style_emoticons/default/smile.gif) I seem to recall a mention of it being inside the trunk lids? Not sure tho.