Ed, it looks awesome. If you're going for DAK, then either a Stug III D or a Stug III F will do, should you choose to put a Stug on the trailer. Should you choose to go the Pz.Kpfw. III route, then your selection is much much larger.
@ Mathew: The trailer was used in Africa, even more, both types, the Sd.Anh. 115 and 116 have seen service.
I hope this helps.