how do you keep surface rust from spreading/getting worse, without cutting or replacing the panel?,

 

if its just surface rust then sand it out.

 

lightly sand the rust off and coat the effected area with a anti rust paint eg: Killrust (Australian brand tho, you will need to find something similar).

 

Ive been using rustoleum rattle can primer, its pretty good, and wet-sandable.

 

I've stripped the surface rust & the area around it to the bare metal, & threw a quick coat of primer on it, so it won't rust while I'm working on other parts of the car,

the part where the rust was is rough, how do I smooth it out so I can paint the car?

 

i duno about paint over there but here primer is not water proof, over time it will rust unless you put a top coat over it.

 

if you leave bare metal out in the rain & weather for a few days, what happens?... it rusts.

the "quick coat of primer" is only temporary, to protect the bare metal so I can work on other rust spots & other parts of the car that need work, getting it ready for paint, once all the rust & stuff is taken care of, the car will be sanded, re-primered, re-sanded & painted with Rustoleum car paint.

 

just put some body filler on the rough part, and sand it smooth.

 

thanks,

should I patch or bondo small holes in the body?

 

depends how small the holes are, if there very small, I think bondo would do it.

 

you might even be able to weld the holes shut. Not too big of a deal.

 

Is the rust seen or hiden?

Because if there are like 1 or 2 holes in a hidden area like where youre spare wheel is clean all the rust up drill them to they are clean round holes, Coat them in a anti rust paint then put some ruber gromits in them that way if water ever pools in that area again (that would have been why it rusted in the first place) you just need to pop the gromits out and you got drain holes.