I have just the bare bones of one of these started. I bought semijoe's frame rails and cut them to 28". I am using TLT axles, and the distance from the center of the front hub to the center of the rear hub is 22-1/2". I am using RC4WD Rosk Crusher tires (the sidewall says "HT 19") and plastic Tamiya Humvee rims, (I wanted to have something plastic to attach a hub to, as well). There is just enough spacing between tires of the 3rd and 4th axles for the 4th axle to steer. The width outside the tires is 8-1/2". I also am using a stock semi-truck front spring setup, although the spring itself is from one of the single-rear-axle trucks, so that the screws that go through the axle can also pass through the spring to hold it all together. I also bought Russ' air-ride suspension for the rear three axles.
I'm not sure yet what it scales out to, as I was trying to enlarge some drawings I found to fit these tires. But, my goal was to build something that would work with 1/16th scale tanks. As my primary reference, I bought the Hobby Boss 1/35th kit for the M1070 and M1000 trailer, and plan to enlarge the plastic parts on a copier to fit the chassis.
I am not nearly up to speed on taking pictures yet. With my kids all out of the house, it's just me and the dawg to try and figure out all this technology stuff - and, I think she's a lot more savvy about it than I am. Sorry about that. Here is a link to a photo of an M1070 that uses the Tamiya Humvee rims (and also tires from it). -Mike
http://www.rc-tanky.com/jine/kracik/kracik1.jpg