There have already been replaced sheet metal heaps but also holes stuffed with putty and I may replace the entire strip of metal at the back on a width of 6 or 7 " to well repair also inside.

For the chemical stripping this company makes a lot of vintage cars, it makes a protection by phosphation after stripping and it's it that does cataphoresis painting immediately after.
if you understand German:
http://www.carblast.de/entlack...hemisches-entlacken/
The disadvantage of media blasting and/or old fashioned mechanical sanding is that they do not go anywhere.
but before having it treated, I remove the maximum of paint by sanding to see and repair the maximum of defects:

