Hi Sean:
My trailer is the rusted heap in Bob carriere's photos above, but, I do have an original box mounted, in all places, on the back of my IHC halftrack. I bought the halftrack from the late (and Great) Bill Gregg and he told me that it was an army workshop mod to make a fitter vehicle for transporting and swapping tank engines. makes sense as the 1/2 tk also has the fittings for a gin pole on the front winch mount.
Anyway, the trailer box is well fitted onto the back of the 1/2 tk and will be easy to measure when I can get at things in warmer weather (its buried inside the barn three rows back in the "some day I'll have time to restore it" line-up!
I will probably have it copied here in Ottawa by a truck body mfr when I do the trailer up. Nothing too complicated- all flat panels and easily bent reinforcements. The tailgate might be the most complex part as it has foot holes in it!
I could likely weld one up myself but on 5 Feb Her Majesty is shipping me out yet again and I will be away until the end of May. I'll still be on net so I'll continue posting.
Hope you don't mind waiting that long.
Cheers! Mike