Doing a great job there, brings me back a few years when i did this for a living. hard dirty work that never seems to end. You are doing the right thing cleaning and painting as you go. Bits get lost easily if you dont.
One point i would like to make to everyone who is doing this, ( i found out the hard way many moons ago)
When chopping and welding so much of the floor pans and panels it is wise to make a temp strut for the door gap one you take the doors off the body (especially a targa roofed car) as it can can move quite a bit, you wont know until you refit the doors and you will be too late then. Im sure you will be fine as you were doing small areas at a time. But do check and strut up if you are doing a restoration.
Another tip if you dont mind. There is a wheel that 3m make that is fantastic for cleaning up rust, underseal, seam sealer etc. Its a clean and stip wheel and its brilliant. Great for the awkward bits and wont carch and split like a sanding disc can, flexible to get right into the grooves and ridges etc.
This is the wheel, you need the middle arbour as well
this is what it does very well
fits on a drill,
this is the area i will tackle for this demo. Not rotting i know but just to show how this works.
This is what it does for the area and for getting old cracked sealer out.
once really clean ( and i do mean clean to keep crap away) you need to protect with a chemical zinc coating. Do this bofore the damp gets at it and compromises the area.This stuff is very good and is only for a light protection coat. and always BEFORE you seam seal so you have prtection under the sealer. A thing most manufacturers never did with disasterous results.
It will look like this once coated with 2 light coats.
Use an acrylic or polyeurathane sealer like this or any good make. These are over paintable and always remain flexable and have excellent adhesion properties
You are now ready to prime with a good 2 pack acrylic filler primer. You can then finish paint or waxoyl.
Hope this helps and remember the cleaner you get the steel the longer the crap stays away.
Ron