I remember working on a truck, the owner drove it on the beach, he had a homemade concoction of kerosene and tar and asbestos fibre, it never dried, i remember it because you got covered with it every time I had to work on it, but never problems with rust
Anyplace that salt moisture can get trapped needs to be treated with something ----between the fenders and aprons ---down inside the body where water going down between moveable windows and the body drains
I would treat all areas with waxoil or a similar treatment----
https://www.tetrosyl.com/tetconnect/...roofing/TWO006-