I’m sure I’m not the first to come up with this idea, but I don’t know why no one has filled this need in the market.
If I want to spend a night or a week in a hotel anywhere in the world, I can enter the dates of my travel along with my other requirements in any of a dozen websites. They will locate hotels that ACTUALLY HAVE VACANCIES that fit my needs. I have found no such service for RV parks. All the websites I’ve found will show you which campgrounds have sites that meet your criteria; but if an area is busy, one can spend hours checking with individual campgrounds only to learn that they are all booked.