Yeah, Mike covered it pretty well!
Welcome to the late 70's trucks! Actually, the whole line up were rot boxes and poorly designed. All marques had their rust issues, but the Dodge sheet-metal seems "cheaper". I make this observation by actually having the different brands of trucks of the similar vintage parked side-by-side.
Fixing the cab rust on the Dodge trucks is pretty easy to do though. But the one place that's really critical, and NOT an easy repair, is the rain gutter above the drivers windshield. Heck, even my brand new (at the time) 1990 Ram truck started to rot up there in 4 years!
The rest can be fixed, and parts are there to do just that. I have drawings for the inner rocker panels and seat supports, which are two items that usually need repair, but nobody makes. If you want them, just let me know and I'll send them to you. Have a local shop make them for you!