Having a go at the rust around the side cargo windows (fixed glass) on my 80 yesterday, and treated the area with Fertan converter after I had enough of physical preparation. Sadly it's now raining but the Fertan instructions do say 'spraying' with water assists penetration. 
Until I can actually get the glass panels out this is all I can do. I removed as much as possible of the really nasty water-based hardware store enamel I'd previously used and will re-do the areas of the body directly under each side cargo window with proper metal primer maybe and follow with oil-based hardware-store enamel.
Being a factory white painted 80 I don't care about 'matching' as the rest of the vehicle's original paint is bad anyway.
Until I can actually get the glass panels out this is all I can do. I removed as much as possible of the really nasty water-based hardware store enamel I'd previously used and will re-do the areas of the body directly under each side cargo window with proper metal primer maybe and follow with oil-based hardware-store enamel.
Being a factory white painted 80 I don't care about 'matching' as the rest of the vehicle's original paint is bad anyway.