Two part primers are well worth the money. They build a much more stable surface, that doesn't swell from solvents, then shink later to expose imperfections and body work under the primer.

Everyone worries about the primer as a moisture barrier, but I guide coat and wet sand the 2K primer on all of my jobs, including "from bare metal" work, and in the last 15 years I've been using it, I've NEVER had rusting underneath!!! I'm confident enough to guarantee every job for as long as you own it...........and I sleep just great at night! :-)