the rust will only come back if you dont grind it all away. depending on how deep it is you might need some bondo, but dont use it if you dont have to. if you dont have to use bondo then prime the area before you paint it. the rust inhibitor isnt a bad idea, but i never do it and i paint all day everyday. you arent going to be able to make the paint unnoticable cause no spray paint is going to give you the finish of factory and chances are if you have rust it is an older car with slightly faded paint at the very least. your best shot is to paint the whole door, but im sure that wont match either, but it might look better.

 

i tried coco cola on small rust spot and it took that sucker off, even the bug crap.

 

As a certified cook, Ive tested the coca cola theory... and to tell ya, that leaves nasty stainds on a grill. I prefer sprite or 7-up. that tends to work better. You should give that a try.

 

Buy a 20 oz Coca Cola, open it drop in an 8 penny nail close it back up, put it up, dont touch it for 2 weeks the nail will be completly dissolved!

It takes 20 liters of water to every 1 liter of cola to even out the acidity in your body after you drink it.

Clutch slippage problems? not with Coca Cola! just take your inspection cover off, shake up the coke aim and spray it on your clutch
Voila you can now get home from the carmelization of the glucose in the pop (it makes it sticky in laymens terms)

a 12 oz can of coke has 16 tablespoons of sugar! . . . Diabetes! red hot Diabetes here! get it while it's good!

no really Rust is corruption. buy a Deloreon instead! they had stainless bodies! or you could wire brush the **** out of the spot primer it
sand it to feathering primer it again, wetsand it with 500 grit or better paint it with an airbrush, wet sand it again after 3-4 coats of the paint