I managed two storage facilities in CO. I spent my days watching 20 security cameras when I wasn't busy checking people in and out. I knew what cars belonged to which people and I knew what units they were supposed to be in. They won't take any responsibility for it, I'm sure, but it went out right under their nose. They do have responsibility in this, morally at least. If there was no sign of forced entry into the facility, then a storage tenant stole your car. They first need to find out who accessed the property on that date and get statements. Did they have to break a window to get in the car?
I had a Pontiac Firebird in the late 90s that was sitting at a transmission shop waiting for a tranny. It got broken into overnight and they stole the stereo and upon doing so ripped the whole bottom portion of the very hard to find dash out of the car. I didn't have coverage for theft, and after discussing with the shop, they agreed to give me a bit of compensation... not full, but it was at least something. It was pretty disappointing to get their call the morning after it happened. It wasn't a perfect car but it was a helluva lotta fun! I never was able to find the proper dash to put back in.