Painting the trunks/engine bay/underside/cabin, POR-15 and leave black? Options

[boxsterfan]

I have been thinking about what I will do with my car in the future when it comes time to restore. On many cars, I see people have appeared to POR-15 (or other) the trunks/engine bay/underside/cabin and then left it black? They then go on to paint the rest of the car as normal (orange, red, white, green, etc...)

I'm not looking to build a concourse winner myself. I am looking to build a car that is restored and protected from rust for as long as possible (another 40 years lets say).

What do people think of POR-15'ing (or any other product) the trunks/engine bay/underside/cabin and then leaving those areas as that? And then (in my case blue) painting the rest of the car as normal?

[Mblizzard]

It is my understanding that POR-15 is very susceptible to degradation by UV light. So unless you are sure the part will never see the light of day, then you should paint over it. Yes it is unlikely that the trunk will get a lot of sun in it while you are driving. But I don't think that the POR instructions give an acceptable UV exposure time before it starts to degrade. If that point could be reached by leaving your trunk open for a few hours it just doesn't seem worth going through all the work to apply and then leave it exposed to the very thing (UV light) that could case it to fail.