Yup, what Pinto1600 said..

It's best to cut out all the rusty/damaged areas & replace them with matching sheet metal or sections from a 'donor-car'. Many good body shops and a few individuals with serious 'talent' in body work can fix that type of damage. But any way you might go, try to get rid of all the rust, inside & out.. even by spray-coating the metal surfaces with a rust-inhibiting paint. (Certainly coating all those surfaces inside & out of a vehicle is not easy, and also why most auto-makers now submerse their vehicle body's, parts, & frames in a rust-inhibiting coating as they now build them and especially before they're painted).

C. M. Wolf