[962porsche]

ok needless to say you need to take the adjacent panel off to get access at all the rusted area.
screw the rust converter crap the only time i ever use it is when you can't clean the rust down to bare and remove it all. and thats hardly ever.
get a little spot sand blaster they are not very costly and get a bag of blasting media. tractor supply has both at very good prices.
at tractor supply look up SKU # 390784599 for the sand blaster it's about 25 $ and a bag of fine black diamond blasting abrasive for 9$ .
once you have blasted the metal spotlessly clean then spray a coat of epoxy primer over the bare metal area. a chromated primer will be best for this but even a none chromate epoxy will work good.
from there if you have a few rust pits you can skin over the epoxy prime with a light weight body filler to fill the rust pin holes.
next spray a few coats of a filler primer.
sand that and then you can go to your top coats.
you said you wanted to keep the single stage. you can still do a blend with single stage.
the problem is knowing how. even most so called painters don't know how to do a single stage blend . side note the are not painters they are sprayers a painter knows how to do it.
i could walk you through the steps of how to do one but not at this time.
1st do your repair then i can tell you how to do the blend.