Easiest method would be sandblasting -- do you know of a local auto shop that does painting - you could probably talk them into blasting it for you. Or you could get some paint remover\stripper from a hardware store that should work also (you just brush it on let it sit for awhile and scrape off )
There are metal paint removers in liquid and gel form.
The only thing is that it can take minutes or hours.
Also the bare metal can start to rust if you don't apply a primer or rust inhibiter right after.
Rinse or wash off the panels with mineral spirits and a soft rag then let dry before painting.