Not that wide, most expedition trialers made here in the states are 70 inches, that would include the AT Horizon. My base camp is 80 inches and have not had a problem so far. Sure I am going to run into one sometime, but if the truck can get through you should be able to get the trailer through.
Great find, and they are truly great trailers. Does it have the torsion axle or is it still the springs. Most likley has the springs that is the reason they are getting rid of them. Either way great find. Have fun man.