Is this "RCPA" (Radio Control Painters Association) going to be official with a board of directors and membership dues?
It sounds like a good idea that would protect members by said "seal of approval" that would set a minimum amount their work should go for related by materials used so the painter doesn't lose money.
It will take a lot of work to get such an association fair and right and all the details worked out, but sounds like your well on your way.