Towing Issues: posting of Restrictions on Parking, different point of view, sign states

Question
What does Restrictions on Parking define? I parked in the parking lot of Palo Verde Storage in Tucson, Az.  Upon entering the lot, there wasn't a visible sign posting rules and regulations on parking after business hours .  After finding out my vehicle was towed, I notices signs posted on the gates of the entrance to the storage units, which secure the storage. I did not block any entrance, I didn't park in the handicapped zone, my tags were current, nor did i need a permit to park.  Also, there wasnt a sign stating do not park after business hours. he business was closed, because business hours were posted. I feel as if this is a shady way of making money off of people that are trying to find a way to spend a Sturday evening at the Swap Meet, which is next door to the storage. My question...Should there be a sign stating do not park after business hours? The only violation I believe I fall under is where the sign states "or other property rules &  regulations".  How would i know this?  Also, I have parked at this same business in the past not having any problems with being towed.  This was a very expensive evening costing us $200.00 to get our truck out of impound... I understand any feed back is strickly for educational purpose.

Answer
The biggest problem is the vehicle being parked on private property especially after business hours. From the property owner or manager's (or acting agent in charge of the property) point of view the vehicle was trespassing and had no reason or official business being there. It's not a shady way to make money, try to look at it as if it was your property and people were parking their vehicles on your property without consent. Think how you would feel watching people park vehicles on your property and walk to a neighboring business or location. Just some insight with a different point of view.