Roofs are a paint at the best of times never mind all those recesses.
as has been said, it will take much longer than you think. a roof like that can take longer than a full side.
You are constantly working leaning over and trying not to lean on the media or damage the van. lots of ways to do roofs, really a self preference and can change from vehicle to vehicle. But make your comfort paramount or you will start cutting corners, which leads to errors.
make sure your media stretch process is correct and the media you are using a good one. personally i would use Avery for that, purely down to ease of use and will deal with that sort of roof.
wrap bar… hmmm i can see how it would help some doing the likes of a bumper. but for me. no… i think its over engineering a small issue. how i can say "over engineer" what is technically a alloy brush shaft … 😆
joking aside, i am not really knocking it, im all for people trying to overcome problems like this, so hats off to them.
that said, a second set of hands for a few seconds will be a better help doing a roof with one of these bars. just my opinion of course.
remember, films like 3M and avery have self levitating adhesive systems so its not sticking till you put it there. a blessing when working on this sort of thing. plus, there is no need to strip the full backing paper. just unroll what you need while pinning it taught with magnets.