How to use mobile air conditioners in RVs to cool down the car?

The mobile air conditioner discharges hot air to the outside of the car, and correspondingly needs to enter the same amount of external wind from the gap in the car, so it is said that the cooling effect cannot be obtained, but why can't we put the mobile air conditioner outside the car (regardless of the factor of theft) to send fresh cold air to the car, so that the car forms a positive pressure, even if the cold wind in the car squeezes out of the car, it will become colder and colder.