Class A with Doubles endorsement, front trailer must be 5th, both trailers must have brakes and break away brakes total length must me under 65'. make sure you dont overload any of the axles and/or the tongue/hitch weights. they may make you prove you are under weight. These guys are correct. The problem is the DMV is clueless as is most of the ...
A doubler is so named due to the fact that it doubles the cost of the rig. This is a result of the breakage that follows the installation of a doubler. CTM u-joints or Longfields, alloy axle shafts, stronger driveshafts, beadlocks, motormounts, output shafts and yokes, ring and pinions, broken links/joints if link suspension etc... By installing a doubler kit you also actually decrease the ...
Think of how a snatchblock works, your cable goes out, goes through the pulley and is attached back to your vehicle with the pulley attached to the "load" this effectively doubles the amount of cable you have to winch in to move your load a given distance, therefore your pulling force is doubled.
Colorado allows doubles to be two bumper pulls (not that I'm saying it's a good idea); many states don't require that the first trailer be goose/fifth. I've heard comment that Colorado limits how long a combo can be, but have never found anything about it in the law books, at least not outside of commercial-trucking stuff.
By the way, regarding the durability of their forged steel crank, Peninsular Diesel claims: "The fatigue factor more than doubles the engine cycle hours." Could be hype...or not. Most all the diesel engines in Alaska get idled a lot. There aren't many low-time 6.2L engines in Alaska.