Not knowing where you’re at (living wise) my brother has many a dodge parts rigs. He got 879,000 miles before “retiring “ his first 98’ or 99’ dodge dually Cummins 12V. The seats are one of his big things he wears out. (Even on his newest one 2014). Normal dodge seat issue is the left side cushion. You’re already up on most of the things. Watch for where they rivet the two main frame sections together. It collects sand and water that will rust them in that spot. Oil coating the frame helps A LOT! NH salts their roads.
You're brother doesn't have a 5 speed swap he wants to part with does he? I'm in SW PA. Rust is the bane of my existence. Now that you mention it, I have seen some trucks rust where the sections of the frame are riveted together.