If the rust is still at the surface and not boring through making big holes, go after it with a couple quarts of Rust-to-leum red rust primer next spring.

It involves a lot of elbow grease, a wire brush, a putty knife, and tenatious will power. Forget about making it look "nice" because with the new addition of crumby looking red primer smeared all over the car, it immediately becomes a cool looking ride which no one wants break into or steal. And you have the great mechanical advantage in its underpinnings.

I pour the stuff into places where I can't reach, rockers, rear wheel arches, wheel wells in the trunk, door interiors, you get the idea. And keep driving it, it is the greenest car on the road, i.e. it is saving natural resources.