If you are having to cook out of a rented kitchen the that will probably put a quash on using your WSM's. Generally speaking, all things used in the food prep/cook/storage/serving has to be NFS approved, and the webbers aren't. Since you are also working under the kitchens HD permit, they probably aren't going to allow you to use a process that will put their facility HD permit in jeopardy. Your county MIGH have some kind of variance the will let the health official make a variance for you since BBQ isn't done in an oven
Here in Riverside County where I am at, the seem to have the most restrictive HD laws in So Cal. and they sound like they might be on par with yours. I have kicked around the idea of catering but it is going to be tough and expensive. Best I got it figured, I can cook at public events like a fair or charity event under a blanket permit from the event organizer. I still have to have my setup of fresh/gray water, triple sink, hot water, cold storage, the whole 9 yards. If I do a private event such as a wedding or BD party, then no on-site food prep. have to use a rented kitchen, all food, ingredients, and utensils have to be stored and used there. Absolutely nothing prepared or stored at home. Basically cook at the kitchen, deliver and serve at the event. Gotta be a way around it but I havent found it yet, so I plan on meeting face to face with the HD to see what we can work out. No onsite cooking takes the atmosphere out of a catered BBQ. Oh, and even with a rig permitted for on-site public events, I can not take the smoker home, it has to be stored at a county approved commissary facility, again more $$.
My wife runs dogs in AKC agility trials and 3 years ago I looked at getting a simple hot dog cart to sell hot dogs at the meets. Pretty much the same stringent rules with something so simple. We did a breakdown of just food costs: Buns, franks, serving boats, forks, napkins, salt and pepper packets, mustard, etc. Everything it would take to put a basic dog in the customers mouth. About $1.75 a dog that you might could sell for $2.75-$3.00. That didn't include commissary rental, travel, ice, equipment, insurance, permits, etc. Not a lot of profit there. From what I see out here, the successful caters also have their own restaurant to back them up. Now that I think about it, owning a BBQ shack might not be a bad idea...
Dedicated Stick Burner, Pitmaster @ All About The Q, facebook.com/itsallabouttheq KCBS CBJ