I've recently done a lot of my back end (on the bus that is, mine doesn't need painting) in POR15 . I spent a lot of time prepping it and it has gone on really well with no peeling.
It does need a bit of work before you slap it on but I think it's worth it. We all spend so much time and money on our busses so I figured the extra time and expense on this was worth it. If it can keep the rust at bay for a few years then it's a bargain.
However like people have said whatever you do don't get it on you cos it ain't coming off. Well actually it does come off eventually. I got some on my face and hands, I wasn't bothered about my hands, I just left that to come off on it's own (about 7-10 days) but I couldn't really go out in public with splops of POR15 on my face. So I gave it a good scrub with some exfoliating pads and once I'd exfoliated down to the bone the POR15 was gone but my face was a bit of a bumpy, red raw mess.
We are going to try Dinitrol for some of the rest of the bus. No idea what it's like but it has some good reviews and recommendations on a lot of restoration forums.