My 06 has the silver gray metallic paint, and after all these years the only rust that has presented itself is around the windshield. That being said, I rarely wax or wash in my Socal environment and once in a while spray it off with a hose. In other climates, I am sure this lack of care would lead to a rust bucket.
I recently bought three kit gallons of Herculiner bedliner that I plan to roll and brush on to my roof and the rest of the van in the near future, now that I have removed the plywood floor of my full roof rack that was degrading after 8 years. I bought some sheet aluminum for a one time fix to replace the floor up there and will add some thick outdoor carpet and padding to soften the space up on top for my star deck.
The silver gray seems to be a good call for resisting rust as long as possible and it does reflect heat as well as any color. The white does not last. Bedliner does.