It's a work truck, so I hope you use it for what it was intended, not keep it in a garage for 20 years. Along those lines, you should get it sprayed with rustproofing goo. That is NOT the same as undercoating, but something like the Ziebart stuff of 30-40 years ago. It works, but it depends on the applier knowing how to get the goo into all the nooks, crannies, and crevices. On an old vehicle like that, it should be easy to get it into the seams and inner panels. My 1973 911 was sprayed with Ziebart when it was new, and then was driven for 20 years and 110,000 miles in Virginia, and it has one of the most rust-free bodies I've seen on an early 911.