Right in your neck of the woods... Bunch's Boat Storage just off Cornellius Pass road just north of the freeway. $70 a month for a covered space. My boat loves staying there when she is not in the water!
The place is a wide open gravel area. Not typical for a storage yard. The guys work in the warehouse on motors and what not, so it seems safe enough. They don't like people to back their boats into the storage areas - just drop em off and they will park them.
I would prefer a place that has 24 hour access and is more tuned to folks that pull their boats in and out on a regular basis. Having said that, your boat may be safer there as they work close to where the stored boats are.
Main plus for me is they are 5 minutes from my house. For the time being, I'll keep the Custom Weld in the driveway.