I'd probably look at one of the ones they have at home depot, it really depends on the gpm you are looking for. With a concession trailer it maybe listed in your health department requirements
Food service requires higher temps than a residential heater from Home Depot will attain. I think 140 degrees is required for food service. Could be wrong, but I would check with Health Dept or Ga Ag Commission. Which ever one will be inspecting you concession trailer.