I use my used up clean n strip discs. The edge of it is abrasive and rips thru seam sealer and paint with ease too.
Or u can carefully use a cutoff wheel. Thats the method i used on this door. It looks to me like u might have to use the top and edge of the wheel to get it in there tho. This all gets covered anyway right?
View attachment 217682used up clean n strips I always save for these tight crevices.
View attachment 217681 It doesn't get it clean completely but alot less to spot blast out. Tbh we'll never get that seam completely rust free since it's embedded between the layers of metal but I figure if you get enough of it out, epoxy it(inside and out if possible) then seam seal and paint, it should outlast us.
Also If I haven't already recommended buying 3 cheap harbor freight 4.5" grinders, and 2 packs of these
BHA Easy Strip Discs Clean and Remove Paint, Rust and Oxidation 4-1/2” x 7/8” - 5 Pack
https://www.amazon.com/dp/B01B8GQ0BW/?tag=gbody-20
I bet I could strip a whole car with 10 of these wheels. By far the most effective tools for stripping panels by hand that I've found. The 3m ones are better, but not by much tbh.