how good is por-15

spell check please!!

....And judging by this statement
"POR-15 is the product that changed car restoration permanently and is used by manufacturers world-wide to protect their factories from rust and corrosion"

I'd definitely give it a go If I were you...

Dunno what kind of light rust you are referring to, but with the (little) experience I've had with bodywork, I would imagine you could just sand it down?? If you're getting it re-painted anyway I'd personally want that rust gone, rather than just stopping it.

Sorry If thats not the exact answer you were looking for

just my $0.02

Where can you get this stuff?

I use POR-15 a lot on old motorcycle gas tanks. There is a kit they sell that cleans out the rust and etches the metal all at once. Wash out the acid... then use the por-15. It works great for this type of application.

On chassis work like you describe I don’t think I’d use it. It would be worth putting the car in the air, going nose to tail, getting the rust 100% gone, and then sealing it back up. I'd do it in sections... you don’t have to strip it all out... just the trouble spots... and once its clean... seal it ASAP. Do not wait.

If it were a 100% drag car were weight counted the most... I’d acid dip the car and then paint everything... but it’s not... if it were a road race car id still say seal the hell out of it. You never know what you'd race in, and the "extra" weight of the sealer is as low on the car as you are going to make it anyway. If it’s a street car... I’d do the same. Clean it up right, seal it up right and you won’t have to worry for years and years.