Fabulous modelling. I hope you don't mind this slightly off topic post but I hope someone can help me out. I've just started building a similar 1/48th tractor/trailer combination. My one is RNZAF in the Pacific with IH tractor unit and an unidentified fuel trailer. Note it has a spare wheel on the rear side of the trailer.
I assume the trailer was ex USN or USMC but it could have been made in New Zealand as I have picture of similar (top of the tank is different) but not identical post war fuel trailer with a spare wheel in RNZAF post WWII use.