I don't know how much of a niche it is. There are a few "we rent privately owned RVs" companies, but they aren't common and they cater to hind-end rigs that can get a great rental rate.
A vacationer is not going to want to load up an RV with gear, drive to a distant state and then have to find their way back to their home with all their gear. They'd rather rent from Cruise America and get their ride back home included.
Your best bet is to find someone who is trying to relocate. They are the ones who will want to load up an RV with all their stuff, drive to another state, and then unload and walk away. But, they likely aren't going to be able to afford the additional costs (insurance, etc.) that they will be expected to spend.
