Outdoor theatres were automobile accessible from inception. And, any business model should prove itself.
Putting in a Home Depot, cannot be any less expensive; and, they can afford to provide space for free.
An outdoor theatre space could be designed to be able to add more capacity from inception; and expanded as necessary.
Pay attention to what others have told you.
You say that putting in a Home Depot cannot be less expensive. They sell something besides RV spots. They have no utilities for RVs. They let people park for free because they may get bussiness from th RV and they get free word of mouth advertising.
You are talking about buying a place that was built with the idea of fitting automobiles in the closest possible space. RVs are larger n automobiles and require more room. You would need to remove the humps that were placed in each row. You would need to remove the posts that held the speakers. Most RVs expand to 12 feet wide how many autos are that wide. With no other work you could offer free parking and may get a few people. If you want to charge you would need to offer things like water, sewer, electric to each site. That would give you the bare minimum of money coming in. Perhaps $5.00 or $10.00 a night which would pay the bills for the utilities used by each site. To get higher you would need to offer other amenities such as a pool, wifi perhaps a putting green or even showers and laundry.
The outdoor screen would just be a tear down as it would have no use.
All of this would need to be on a highway that was of use to an RV person since they will not go out of their way on some back country road to get something that they can get at a normal campground.