Most storage places won't let you work on them in their lot.
I think it just depends on how much noise you make, the neighborhood...here's a thought...how about a salvage yard? Way back out of way? Rental lots in industrial areas...I'm gonna be in the same spot you are when I get a bus...This varies a lot.
In my time here I've heard that U-Haul storage tends to be relaxed about that if you leave no mess.
Lots of private storage facilities too that are full of RVs. A friendly chat with the owner might produce results if he/she likes you.