This is the start of my bay. This gives a bit about undercoats. They are almost as important as the top coats. Every peeler you have seen, is a result of mismatched undercoats, someone trying to cut corners or costs.

My bay was bad, like every other bit of this car.
we spent days inside blasting and cleaning.
it got Por 15
a mist coat of kondar prime
full coats of kondar once fully dry
spot prime with diamont dp21 tintable prime
more dp21 finally some color
and clears, the first stuff was bad, I'm trying to use up stuff I've had on hand for many years.

In the ppg world, I would recommend using DP40, it's a light green epoxy prime as an undercoat. I'm pretty sure you can wet on wet it. (spray over without full dry time) Why? undercoats promote adhesion and provide a bridge from old substrates to new. They help color holdout and durability. I used deltron on my friends lawn trucks subject to a ton of chemicals, and held up for years with no issues. You can even wash it with acetone with no problems.