There are good rust-free older diesel trucks around if you search around. Whether you want one or not is a different story but they certainly are more fuel efficient then gassers when pulling trailers.
I drove a 2002 2500HD ton Chevy with an 8.1 pulling a gooseneck horse-trailer. Got 8.5 MPG on the highway. The owner told me when he pulled a 14,000 lb. trailer he got 5.5 MPG.
My 1994 Ford with a 7.3 turbo IDI pulls the same horse-trailer and gets 12 MPG. Gets 17 MPG empty.
Paid $3300 for it 12 years ago. Rust free from Colorado and now has 240,000 miles on it.
My 1992 Dodge with the 12 valve 5.9 Cummins pulls the horse-trailer and gets 13.5 MPG. Gets 20 MPG empty. Paid $3500 for it 8 years ago. Rust free from northern Maine from a place that never uses road-salt - just sand. Has 160,000 miles and runs perfect.
My 1983 Suburban with a 6.2 non-turbo diesel pulled a 5500 lb. trailer 2000 miles and got 13.2 MPG. Not great - but it is an old tech diesel and still better then most gassers could do pulling the same weight and wind-resistance. This was a high camper trailer that acted like a big sail.