The thing about the commisary is to make sure any food prepared is prepared in a health department inspected commercial kitchen that is zoned for that purpose also.Uncle Vic has a good suggestion about a local church,VFW,or some other non profit group that would most likely not mind renting you the space as needed.Although a cart is less expensive,a concession trailer with hot water,three bay plus hand wash sink etc., commercial refridgeration,washable surfaces and inspected by the health department to prepare foods usually does not require a commisary,since the concession trailer is the commisary,not so with an open cart.Some health inspectors are more lenient than others,some are like drill sargeants.The reason some hot dog vendors with open carts are not required in some areas to have a commisary,is that all the food is bought prepared,premade by a distributor,even the hot dogs are really cooked when you buy them they are just ,for the most part warmed in the hot water.The same with the toppings,they are just being warmed in the steam table.The one thing that all health inspectors that I have come across stress is that no food can be prepared in your home kitchen(unless it is a commercially licensed kitchen),but many vendors do,but it is something that they don’t allow.It is better to do your research before you buy a set up,then to buy something first ,and find out you should have bought something else,like many people do.That is one reason you will see hot dog carts for sale on ebay or elsewhere pretty cheap,is that it was more of a hassle then they bargained for when they started dealing with a strict health inspector,or found out that some areas do not allow mobile food vendors,or you need a permit,and most if not all the permits are taken and it is impossible to get a new one issued.I am not trying to discourage you,I am just complimenting you on doing your homewaork first before buying something and jumping into the business unprepared.
Good Luck!
Jim