Wow, what a plan! I don't do vending or catering, but as a customer who frequents food trucks & trailers, have you considered a fold out awning on the customer window side. i'm thinking if you make the ordering/pick-up window a comfortable spot (Texas sun & rain) compared to competitors it might just increase your business.
Weber 26.75 OTG w/CI grates & SJ/WSM Mini
Home built 24"x72" reverse flow stick burner trailer with 18"x44" grill w/CI grates and upright SS gas oven/smoker.
Home built 48" fire pit with a 30"x30" Santa Maria style ranch grill.
Home built lump charcoal retort, iGrill & a bunch of other cooking toys.