2k primer is good (and the right choice to cover your bodywork) but now you need a good epoxy primer (we use Extreme).....but any good epoxy high build primer will do the job.
Yes, I am a professional painter....(but don't let that get out, as I am trying to be RETIRED!...and work "MY" Teardrop Trailers and Street Rods!)
Because "Topcoat" paint is so pricy these days.......you do not want to cheap out on the undercoat! Remember... Paint covers nothing!!
Your paint job is only as good as the prep work!
Follow your heart......Brian