Convenience is key, for both you and your customer.
Take a look at Sitelink or Easy Storage Solutions as a software partner. Software is going to make or break that convenience factor. Be prepared to spend a couple thousand on a gate system and $40-$60 a month on software / merchant solutions.
My facility is setup with an electronic keypad gate for entry and exit. Customers can rent a unit 24 hours a day by pulling to the gate, hopping on the website and completing their digital lease agreement (hire a lawyer) and entering payment information.
There's no paper lease agreements or cash exchanging hands. No credit card or ACH account, you don't lease. Everything's auto pay only.
All the empty units are locked with a word lock disc lock. This allows for security of empty units, as well as allows the computer to email the customer both their gate and unit key code. That way I've got access to the unit in the event of fire / flood / emergency, and I'm not meeting up with someone just to hand them a set of keys for their unit.
The reason for an exit keypad and not an automatic gate with a sensor is twofold. It prevents people tailgating someone else in, less they're trapped in there, and secondly if a code "signs in" but doesn't "sign out" within a specified period of time, I'm alerted on my phone which prompts me to check cameras and identify why someone's spending so much time in there (sleeping, running a business, maintaining vehicles, etc).
Our exterior RV spaces are 10x50 with 30' travel lanes. Remember these aren't professional drivers you're dealing with here, more room is better. Your climate may dictate different, but in Tennessee with the extreme summer sun majority of our customers are looking for covered parking (think lean too / carport) which account for 80% of our outside spaces. Many of our customers elect for 30 Amp hookups similar to what you'd see in a campground. These are individually metered and power cost is marked up by a few points.
I've got 15K square feet of inside storage and we're adding an additional 10K by the end of Q2. I've owned the place since July of 16' and purchased it as an established 5K square foot facility in neglect. It's considerable hands on work in the beginning, but once you reach the autopilot stage it has it's benefits.
Feel free to PM me with questions.