How long will it take you to assemble the truck, and what kind of primer are you using? Epoxy primes seem to stop rust from forming under primer better than other kinds. If you're like the rest of us and will take more than a week or two to assemble, I would recommend putting at least one coat of paint on everything before assembly, and finish coating what can't be painted later at that time. Then assemble the truck, sand and finish the paint job.
