Do you seek or get permission from the owner? Do you obtain a search warrant? Don't you need "probable cause" to get such a warrant?.
Is this also true if you tow a car for a parking violation?
With parked cars we can tow them if they are a hazard, if the registration is expired or if they are abandoned junk MV's. If the car is locked up we generally dont search them too much, just write down on the inventory sheet what we can see from the outside.