i just want to make clear for the record.
If the car is just dingy looking, leave it until you can get good body work and paint.
If you have surface rust, bare metal, etc. and it is going to be a few years or more till you can get good body work and paint. do the minium prep and body work to address the rust, then use roll on or spray on rustoleum.
you are looking at around one hundred bucks or 150$ or so worth of expenses.
I had this to deal with...
it lives outside and I did not want to let it progress as it may never get good bodywork and paint.
if it had been just dingy, like some of the other areas, with no pitting and base paint still intact, I would have just waxed the hell out of it.
while it looks great from ten paces or driving by (in my opinion), it looks like what it is the closer you get
some can get great results with this type of paint job, but it takes just as much prep as a real paint job. you can see I just did bare minimum prep to address rust.