I know that lots of people use POR-15 or a rust conversion product for their floorboards, but since my car is painted white inside and out I was thinking of using POR-15 Whitecote. Any thoughts?

two thoughts: POR15 is POR15 & POR15 can also be painted

and your going to cover it with carpet
so you are the only person to see it

BTW mine is and was always red but my floor is white