It’s for campers and trailers, where people can park them to camp for the weekend, and (maybe) permanently keep them or at least for a lengthy amount of time for storage. There are certain laws against keeping a large RV in your driveway or on your own property for over a week.
I think you are confusing RV parks with RV storage a bit. There is a lot of differentiation in the RV industry, at least where I live, and RV park means a place where people can live out of their RVs for an extended period of time, usually weeks or months. This is distinct from a campground, where RV owners can only stay briefly, usually for 14 days.
Think of campgrounds as normal hotels, whereas RV parks are like extended stay hotels or apartments. The latter can have places where campers can receive mail in secure mailboxes, as well as other living amenities.
Campgrounds where I live can be public or private, and many of the private are owned by KOA. Contacting them to set up a franchise might be a good idea.
But all of this ignores the elephant in the room - the biggest expense for RV park owners is land. You need space for your customers to park their vehicles, but you also need space between the slots to give each owner some breathing room. So you need to buy up a lot of land that is contiguous and that is legally useable (zoned) for the purpose of parking RVs. This land also needs to be close to the city to allow your residents to buy food and other necessities. Your land also needs to have access to city water, sewer, and electricity while being far away from residential houses - those owners don't want RVs as neighbors and may start litigation to halt your business.
Speaking of the law, RV parks can fill up with poor folk and people on drugs and the down-and-out in addition to seniors, though. Your business will need liability insurance and firm rules to limit noise and bad behavior. Cultivating a positive relationship with local law enforcement will be an advantage - consider donating to their support organizations.
RV storage is a very different business - that's just storing RVs when the owners aren't using them. In that case, you can park them tightly together on a small amount of land or get a parking garage built if the prospect is good enough. That is similar to a self-storage business model and so that model is worth researching.