[78K20]

Well, my 1978K20 has to set outside cause my shop is crammed with other collectible stuff. I don’t have a magic formula for you though. I mainly use this truck to plow snow, and haul firewood. I’m located in Northern Indiana. Winters here can be brutal. My last plow rig was also a 78K20. It lasted about 15 years after a re-do. I’ve learned a lot since.
I now clean / sand the bottom of everything / epoxy prime / and I’ve had pretty good results with “Rustfree” as a topcoat. It’s very important to coat the inside of everything with a coating of your favorite material. I’ve used several brands, I snake a hard plastic wand with a special brass tip into channels & coat. It’s important to get something that will run into tight areas. Then, I seam seal all the gaps. I’ve had pretty good results with my daily, and my wife’s car.