Regardless of the discussion of to slide out/not to slide out, keep in mind one thing; there are cities where it is illegal to park/stay overnight at all. In this area of northern Colorado, some cities prohibit any overnight parking and the local police departments do enforce that. In others, it's not an issue. The same holds true for other areas of the country.
Besides checking in with the store manager, it would probably be a good idea to ask him/her if it's prohibited by municipal ordinance and if the manager doesn't know, a call to the local police department will give an answer to that question. It could be a matter of, do you want to be awakened in the middle of the night and told to move, or not?
