I've been using the 3 step rust program that Eastwoods offers. I find that their Rust Convertor, Rust Encapsulator, and Chassis Black works real well in the Northeast with snowy, salty roads.
I try to keep all the sheetmetal dry and clean. Once a year (spring), I do a top to bottom, front to back, and complete underside (including the engine oil pan rust problem) inspection program of my truck.
I make notes where I need to pay attention, and plan according for the repairs.
Hopes this helps,
Butch Cassidy