The workhorse tool when I'm doing fiberglass repairs is a
DW402 4-1/2 inch angle grinder
36-grit sanding disc on a
rubber backing pad, I can quickly grind away fiberglass to replace
deck coring or make other repairs. I've mostly used this tool for such
repairs and, in spite of the coating of abrasive fiberglass dust, it's
still running fine.
I have used it with a diamond blade to cut a freezer in half, lenthwise, to get it out of the basement. (The door had been added after this International Harvestor freezer had been moved in, and the freezer was bigger than the doorway.) It made a bit of smoke and noise, but it made short work of that old heavy steel freezer.