I would suggest that you take a look structurally first, and if the truck is well reinforced, then go to Steel Rubber Steele Rubber Products - Quality Crafted Automotive Rubber Parts and Weatherstripping or Soff Seal SoffSeal Weatherstripping & Rubber Details go through their catalogs then install something that looks like it should work. Yeah, might not be pretty, but even quarter mill cars like Ferrari's and Lambo's have rubber seals.

Makes me wonder if those doors should have items like mine - about 1/2 way down. A tapered slide goes into a slot in the door that has rubber cushions and called dovetails. Look in any Ford resto catalog like MAC's for them- a good part number for a male dovetail is 40-35577 with female counter parts also available. My doors, and on a roadster have virtually no vibration although I also added a lot of tubular steel framework to cut it back as well even though it is a steel bodied car.