What is the best way to remove a thin layer of undercoating in the trunk area where it's getting repainted???

I just got done removing a heavy undercoat off the inner fenders of my 64 300. I used a hand torch and heated/softened the udercoating then scraped it off with a dull chisel/stiff scraper. Cleaned the rest off using a pre-paint prep/cleaner, hit the whole inner fender with a red scuff pad then primed it.

Small torch and scraper. Not as bad a job as you think once you get the "rythem".

a heat gun works too. not a hair dryer. wear a glove on your scraping hand.

I agree on the propane torch and scraper , it's not as bad as expected .
Harbor Freight has a cheap torch with the tip about 2 1/2 - 3" wide. It worked better then a regular propane torch when I did my Cuda with factory undercoating .
remove carpet, wiring, etc on the other side also
wear gloves...... The stuff will fall off in sheets
Donnie

Follow-up w/wiping down w/lacquer thinner or equiv.

Did the torch and scrapper on my Challenger. Lots of time but not too bad