Por-15 on roof

Whatever option you choose, just don't attempt to encapsulate the tiny rust pits on your roof with any type of paint product. Use whatever type of gel/liquid rust remover to ensure you have clean metal and then epoxy over that. Too much time, work and money is involved with a vinyl top car to skip a step and roll the dice on seeing bubbling under the vinyl after a year or two. Especially when the options to fully remove the rust are dirt cheap and don't take a ton of time.