Look at govplanet.com. They might have something similar you can reference for dimensions. It looks as though a specialty box fits in the middle, such as a generator unit, welding unit, or such. It could also just be a cargo carrier. The smaller M105 cargo trailers are roughly 14x7 and weigh 2760 lbs.
"I was called by the Yorkers a outlaw, and later by the english a rebel" Ethan Allen