Technical THIS IS WHAT PRIMERED CARS LOOK LIKE IF NOT PAINTED

Isn't that why they use epoxy primer these days ?
I "was told" by a shop that blasts, builds & paint high $ cars that's how it's done now. The epoxy primer serves as primer & sealer. Then mud goes on top of that.
This was probably 15-20 years ago.
That said, I couldn't afford or trust anyone else to paint for me. If I did my own I fully agree with stick with one line of products & follow the damn instructions mindset.

 

Check the frame and undercarrige.