I finally got all the paint removed from the flat sheet metal
The Aircraft Stripper works pretty good, but it took 3-4 applications.
I wore a good paint respirator, and had the exhaust fan running
but after a while the fumes still get to me and I got out of there for a while.
I used the Aircraft stripper inside the doors and quarters to remove
the thick undercoating from the factory. It worked pretty good on that too!
The remnants of primer that remain will clean off easily with the DA and 80.

I cut out the two quarters and the battery tray area today
I snapped a chalk line 3/4" above the side brace and cut them off
at that point. I also removed the braces so I could straighten
them and clean them and behind them. I cut the quarters at that
point so I would be able to grind and finish the inside too
I was able to cut them of within about 3/8" of the bottom lip
with the plasma cutter, and I used the angle grinder to clean up
the rest of the way to the bottom. As you probably know the
factory used a continuous electric weld, like a spot weld, along
the bottom. Since I don't have that capability, I'll cut the new
panels approximately 1/8" short of the bottom and fill this area
with weld and grind it off flush with the surface.
It'll be completely watertight and will look exactly like
the factory product when I'm done. Before the quarters go back on
I'll complete the installation of the new battery tray,
make new back bumper mounting plates (if you didn't notice
in the picts, I removed them too) and sandblast all the newly
exposed areas.