Not sure if you have found anything yet. Here are a few places to check:
Anchor Storage in NKY.
https://www.anchorstorageusa.com
We previously lived in Union, KY and we looked into Anchor at that time. Seemed like a great place with a dedicated wash bay, dump station, etc..
On the west side is Premier RV & Boat Storage
http://www.premierrvandboatstorage.com
This is another great facility specifically for RV's. Unfortunately they had one of their buildings catch fire a few months ago. The overall facility survived, but they lost space and they have a long waiting list.
Thankfully we were able to rent a spot in West Chester close to our home in Mason. We are at Lakota Self Storage. They only have a handful of garages for large RV's. We actually got locked in while they were under construction. It's tough to find something. Best of luck to you.
John