Treating repaired rear traveller wings

[PeterCat]

Our Traveller came with the back body removed but a new set of wood so it will be a journey of discovery getting it all back correctly !!
I guess we will be doing a fair bit of loose fitting just to see where it all goes.
Current issue is the rear wings. The ones that came were beyond repair so we bought a decent used pair and have carried out the small welding required. There are still some surface rust areas on the inside, these have been wire brushed but pin hole craters remain, In the past I have treated these areas with a rust converter and then removed the surplus leaving ( I hope !) just the converted spots in the pin hole craters. I would then just use a zinc rich primer and paint.
I understand that epoxy primer is now favoured rather than zinc rich or etch priming and will value opinion on this!
Once that is done I will find some good treatment for water and stone chip protection, suggestions welcome.
I see that the wings should be mounted to the frame before fitting frame to car ? I guess that a 'trial mounting' will help me in positioning the wing to frame so that it all fits when the frame goes on the car? I wonder also about painting the wing outer before fitting to the car? If I try to paint when fitted will there be issues painting up to the wing piping? If I paint before I am concerned about damaging the paint work when fitting! I guess I could prime and paint the edge where the piping sits before fitting and blend into that after fitting.
Sorry to ask so many questions but your advice on any of them will be appreciated