I'm curious about the storage location for the spare. Does ER make the indentation in the rear wall of the cabin according to the size tire you originally order on the vehicle? What happens if the original tires match that recessed cavity, but you later decide to upgrade to larger tires? Can that cavity be enlarged; do you put the spare somewhere else; do they make that cavity for the largest possible tire you could ever have at the original manufacture of the vehicle? If they make it for the 41", but you go with the 37", is there a spacer to fill up the empty outer section?