craftgrrl | paint to use on vinyl shower curtain/liner (Reply)

Hello, all - new member and excited to be here. I did search faq/memories before posting, but didn't find specifically what I'm looking for. I am collaborating on a project painting a design onto a shower curtain *liner* - one of the clear plastic ones, not a fabric shower curtain, which would be a different animal. I know we need to use something not water-based, so it won't wash off, but I'm concerned about how the shower liner is flexible and gets scrunched and unscrunched regularly - I'm wondering if most things would crack and flake off, which is obviously undesirable.
Originally I thought oil paint (won't wash off) - but that dries hard so I think it would crack/flake. I had thought maybe spray paint would have some "flex" to it, though I'm not really sure. Someone suggested fabric paint - which I would never have thought of, and which does have flex and shouldn't wash off - but would it adhere well to the vinyl? And it's pretty pricey for doing a whole shower curtain. Someone else suggested window paint, but I'm concerned about the crack/flake factor there.
If anyone here has experience painting on something similar and has suggestions, ideas, or advice, it would be greatly appreciated.
thanks