What's special about a food truck with gourmet sandwiches ??? Take a look at Food trucks and pods in Portland,Oregon. Portland is a real food/foodie truck city. Take a look at their menus and what they do well. If your looking for success in this business you need a standout signature item. Things like a killer Cuban sand that you can't get someplace else.A Killer Torta, Second to none Philly steak sands. OK, you get my drift. Your menu will be a few items and they all need to give people a reason to stop. I'm just saying, be creative, be different but, realize people need to understand what your serving. Just serving gourmet sandwiches doesn't necessarily say something. What will set you aside from everyone else in town ????? take care.......ChefBillyB
That is way to broad a question to answer. Yes, they can be profitable...any food business can be profitable. But, like any business, it must be properly managed to turn a profit.
Like flipflopgirl said, you'll need a business plan, projections, etc. A better question would be, given your area, competition, expected clientele (among many, many other concerns and questions) is your idea FEASIBLE.
If you want more specific advice, posting more info (expected menu, pricing, location, etc) will help.