Painting Vinyl is ok with the correct paint. Vinyls flex and so must your paint, particular low end brands are not suggested because of the resin with in the paint making it more ridged. Higher end brands will not only stick but flex with the movement over time. Pick a high end brand like Sherwin-Williams Resilience, not only will it stick but it will dry to moisture resistant in 2 hours (good if you live in an area that can't always predict the rain patterns). It is also flexible and easy to apply. Now for the color: shhhhh no one is suppose to know this but I do. The tint black that is added to the paint to make (and most colors have black...even when they are white) is what causes the warping of any plastic (vinyl etc). Colors can be made with combinations of raw umber, magenta, and new green to great the look of black but have to be specifically formulated to do so. Sherwin Williams offers a vinyl safe line because of this...all they do is leave out the black. Stores that carry high end products like Benjamin Moore, etc can and do know about these issues as well. Just ask the experts inside.