I've got a 1984 GMC Sierra Classic 1500 RWD. Paint is in good shape but has some rust at the typical spots but that's fine because I'm a welder. I live in Michigan. It runs and drives good with 160k miles. It's on its 2nd engine and transmission. Under the hood is a target master 350 small block v8 with Edelbrock intake, manifolds, valve cover and carburetor. How well built are these trucks? I plan on trying to keep this for the rest of my life.
Frame has a little bit of superficial rust but it's solid .
You should be able to keep it going pretty much indefinitely as a weekend toy as long as you're willing to maintain and repair it as needed and keep rust at bay. There are certainly 50-60 year old and older vehicles still running around.
They're well built but you're dreaming if you want to keep it the rest of your life (unless you're already 80 years old)
I'm 21. It will be garage kept most of it's life and drive it as a weekend toy.
I guess if you don't drive it a lot and put a lot of miles on it, then it could last a while. It'll take a lot of work to keep the rust away in Michigan. It might become difficult to find parts for it. Well what the heck... give it a go.