We have been storing our current camper in two different facilities. I have personally been very pleased with both. The first one was a dirt/grass parking area (with a slight incline). The good: large spots. I would say they were around 20-25' wide and a good 50' long. Also, very inexpensive. The bad: It was about 25 minutes away (just far enough to be annoying at times) and insurance rates were actually higher in that city. The current setup is nicer. Sites are paved, but they are rather tight. 10x40. Doable but tight. Oddly enough I actually like it during storms as the wind is buffeted on either side of my camper. Insurance rates lower since it's in the same city we live in. Much closer at around 7 minutes away - much easier to check on things. Both facilities had security cameras though I like the current one better as they have huge screens at the main office as you go in so you can see the traffic within the gates. Price-wise, they are a little higher but worth it for me.
My requirements for storage:
1. Price
2. Security
I hope this helps.