Painting Over Existing Paint

[RodC]

I had this in Paint & Body but there seems to be more traffic here

I am in the middle of disassembling my bed to replace the wood and coat the frame with POR-15 The paint is in good condition with a few exceptions. Some chips and the fenders have the small flange rusting off in a few places. The truck looks like it was painted about 4 or 5 years ago. however they negelected to paint under the lip of bed and there is about 3 inches of surface rust on the bed sides.

The paint is not so bad that I would like to strip it but I want to paint the areas I fix and freshen up the rest of the paint to make it match. I plan on using Acrylic Enamel.

Heres my questions, If I paint over the existing paint, should I primer the whole panel, or just rough up the old paint?

What kind of primer should I use? Etch, Epoxy? Should I use the same on the bare places I Repair?

Thanks in advace, I have read so many confilcting reports, but we all know this is THE source!!!!