How well will PPG DP-40 hold up without topcoating

DP40 is an outstanding epoxy primer. It has been around for many years. I've used it on a Honda Civic cowling, not topcoated, that was outside in NH weather continuously for about 10 years w/o any rust showing up. That was directly to a sandblasted surface. I don't believe there is a better bare metal primer in existence. If you are going to sandblast the parts to a bright metal blast condition, I would not bother with any type of metal prep, as long as you can apply the DP40 the same day. BTW, DP40 is an old designation. The newer one is DP40LF, the LF portion signifying a lead-free product - it's the same grey/green color though and now there are two different catalysts available (for the LF version only). For your purposes I recommend you apply two full coats after blasting. Be aware that epoxy primers have a topcoat window. That means after 7 days for the DP, the surface will have to be scuffed and another coat of the DP applied before topcoating within the 7 day period. It's not a big deal. Other epoxies have different, shorter windows - the 7 days are for the old DP and the newer DPLF only.

Rod