Rust is a fact of life here in MN. I don't like it and I fight it but it always wins. Always. It doesn't pay to keep miles off your vehicle in this country better to drive the wheels off of it and let the mechanicals and body die in the same century
The best thing I have found for the door and tailgate seams is to spray them with the Amsoil (don't start on the amsoil stuff) heavy duty rust protector which goes on thin and sets up a very waxy film when the carrier evaporates off. Shoot it inside and let it drip out.
I had my Dodge Ziebarted and it helped but, IMO, their guarantee is worthless and taking it in every year buys you little additional protection over the initial treatment.
I have seen several 2nd gen trucks with rusted cab corners, door seams, rocker panels, rear wheelwells, and tailgates. Soon enough I will be driving one. I just sold a 93 Toyota that had rusted at a much faster pace than my Ram is going.