The parking pass you use for parking at the cabins is the same parking pass for getting parking free at the parks. It just stays on your dashboard. I would think if you have a second car that would need to be in the overflow lot, the parking pass would be the same. Especially as people might switch what car they park at the cabin.
Technically the rule is one car parked at each cabin. The parking pad is not especially large. Depending on the size of the cars, it would be almost impossible to legally park, meaning tires only on the pad and not in the grass or road. I had just enough room for the minivan and golf cart.