The rental car sure makes more sense to me then upkeep on a vehicle you use 2x a year for a week or so.

Past that, I had a 4x4 truck that only got used a few times a year, when not in use, it was parked on the grass on my side lot. Grass is about the worst parking surface for a vehicle to sit on long term. Even on the grass, it took almost 7 years before the rotors were damaged enough to have any effect on function, the truck body and frame were in worst condition then the brakes ever were.

If he buys a "new" car to have sit, maybe buy an extra set of rotors to sit on the shelf inside of the building, to replace the original rotors after then get bad enough to need replacement.