I thought you needed a bed and head to licence as a motorhome? You could probably get enough in the back seat to get past that hurdle. You could also just license as a heavy duty truck. I doubt the fire truck aspect matters much. I'm no sure if they require decommissioning of lights/siren or if they are allowed to stay but you get in crap for using them. Similarly, I think you have to paint school busses a different colour than chrome yellow. Not sure if they would want you to make this truck not red or yellow to minimize confusion.Probably but why? License as a motorhome good to go.
Sent from the future