has anyone done this paint the por-15 on let it dry then scuff or sand it. then shoot primer and do base coat clear coat and if you have tell details such as what grit you used on por-15 and did the primer and paint stay on or was it just a waste of time.

I have used it several times on the underside of cars; the most recent is a 69 Barracuda which I just finished.

On a previous cars that were done a couple of years ago ir did it as follows:

I brushed the por-15 on the chassis; within 72 hours of por-15 application I sprayed primer; after the primer dried I sanded the primer; then sprayed my basecoat/clearcoat.

It held up very well.

On some 60's GM vehiles they were deliveried with only primer on the undersides of the body. Putting the por-15 on first to protect the body and then the primer for the proper look finish.

I did it in the trunk of my Cuda. Scuffed all areas that were smooth real well then POR15, POR15 primer, then sanded and shot wuth dupont base/clear. Its fine.
How important using the POR15 primer, as opposed to others, I do not know.

Not to start a POR 15 debate, but I learned to stay away from it.
Zero-Rust for me now.

thanks i was wondering if anyone had done it. so wetsand or scuff i figure 400 grit dried por-15 then shoot primer and base/clear and this should be fine. this is not a show car but i would like the engine bay to be the same color as the outside.

I personally don't care for POR-15.It is a good product but is not user freindly it take to long to dry to go on to the next step.Although if used properly it offers very good protection.Depending on just what you are doing to the car I would recomend using epoxy primer.It is more user freindly.Many restoration shops will say the same thing about the products.
Good Luck Sam

Being a resto forum I would say fix it properly. If it was a general forum I would say it's junk.
But, that's just me.

Where can Zero Rust be purchased?

I've had great luck with Zero Rust as well.