I went crazy trying to find a WWI era German truck a while back to do a diorama of a photo I saw of a Fokker E.III being towed with everything in it's "for shipping" configuration. I had no luck at all.
I did come across these from AJP Maquettes and they may be helpful. Not cheap by anybody's standards, and I have no idea of the quality, but right now, that's all I found. I think I could have tried to convert one of the Daimler trucks to work for me, but if I was going to do a lot of scratching, I didn't want to spend what they were asking.
Document sans-titre
In railroad scales, O comes very close to 1/48 (1/45, I think), so you may be able to find something from the rail stores. Some of their higher end vehicles are very, very nice.
If you do find anything, please let us all know.
Chris