I am not in the food business, but have considered investing in a mobile BBQ business. While I think food trucks are a great business model, I am not convinced that a BBQ food truck is a successful business model. My thoughts are:
Most mobile BBQ businesses that I see have one or two locations that they work from (along with catering jobs they pick up). For example, they may work a large manufacturing facility for lunch, and then move across town to the same convenience store parking lot in the evenings/weekends. I don't really see highly successful BBQ 'food trucks' that set up at different sights every day.
The common thread that I see in the successful food trucks is that they serve 'handle' food. They serve menu items that can be held and eaten with one hand - such as slice of pizza, something served on a bun, or served in a wrap, or served on a stick. Good BBQ really needs to be eaten at a table with a side and utensils. Having a food that requires a table and silverware to eat takes away from the magic of the food truck.
While a BBQ sandwich can be a great value item on the menu where traditional BBQ is served, I think a menu of only sandwiches is too limiting for someone serving quality BBQ product. I am always skeptical of a mobile business that is serving BBQ sandwiches, as I am automatically expecting cheap shredded meat in cheap sauce served from a crockpot - and it is usually just short of inedible.
In fact, I submit that a good pulled pork sandwich, by the time you have sauce on it and coleslaw on it (yes Virginia, even if Santa is not real, a great pulled pork sandwich still always has slaw) it is too messy to be a good 'handle' food.
The old days of setting up in the grocery store parking lots are long gone. They do not want you poaching from their deli business. But I still think you need to find a great location with high visibility to set up your mobile business and work that location for all it is worth. Or find a couple of busy bars with no kitchen and work a deal with them to set up outside on weekends.