......Is there a product that you can treat rotors from rusting on a car that sits a long time ...what to musems use ?

No,cast iron.

WD 40, Gibbs, etc. Just clean it off before you drive it again.

I plate all my rotors so the areas that never see the brake pad never rusts..

Rotor hats are one thing. I will usually paint rotor hats with a grey brake caliper or wheel paint prior to installing them, which always looks "correct" on a Porsche in my opinion.

Museums are usually climate and humidity controlled buildings, so brake rotor rust would be difficult to form,as long as things aren't being splashed with water frequently.

As long as the car isn't being stored 100 yards from the ocean, surface rust won't be that severe or hurt anything.

Several brands now offer rotors that come plated (some Meyle) or painted (some Brembo). The coating is immediately worn off the area swept by the brake pads, but the rest of the rotor stays looking nice. And any surface rust on the swept area gets cleaned off when you drive the car.

Simple solution

the car