use a self-etching primer after you have prepped for painting. I bought a few cans at my local auto parts store. I recommend using Parkers duck boat paint. I wanted a non-refective cool to the touch paint for the inside of my boat. I went with the duck boat grey and it worked great. I ordered it over the phone and had it in a few days. cabelas also carries it.
Plenty of users of the product on tinboats forum also.
This is the interior of my boat painted with Parkers
The exterior paint is undercoated with self -etch primer also but with tractor implement paint bought at the Co-op. Its held up very good.