I'd say if it's been essentially a southern truck since new, then it will last several more years still before you get rust through, even in the rust belt.
Get some rear fenderwell liners if yours doesn't have them. And some good mud flaps.
Touch up all the bare metal chips in the paint, pressure wash the undercarriage if it's caked up with dirt, and get under there with some black spray paint for everything that doesn't move and fluid film for everything that does. Pay attention to painting around the inside of the fender wells and back side of the rocker panels.
I usually wait for an opportunity after the truck has been through some big rain storms on the highway, cleans up good enough for paint to stick perty well.
My 07 has been though 6 of it's 9 winters in the CO mtns or AK and is holding up very well. I burn through a couple cans of spray paint every other year or so.
I don't prefer the mess of fliud film on everything or oil spraying the undercarriage, but there are places there in the NE tht will still oil coat the undercarriage if you're good with it.
