Spoke to someone who used dip to do whitewalls. If you prep the area, it holds very well.
Problems are:
- It goes brown in a week from brake dust and is a bitch to clean. Apparently it's easier to just respray over it, so it's not a convenient long-term solution
- Making a stencil is a right faff and there's a chance of leakage
That would explain why mine flaked off, I never prepped my tyres since I never intended on spraying them