I finally bought the tri-fuel Yamaha and all the accessories to hook it up.
First, I bought the NPSK kit (12' hose and regulator) from US Carb. I replaced the POL fitting with an Acme nut to make it easier to hook up to a portable cylinder at home for power outages. On the other end, I put a quick disconnect that matched the one on my trailer.
I then added a 3/4" elbow to the generator's regulator input and attached the 12' hose. On the other end of the hose, I attached a nipple compatible with the QDs on the trailer and bottle regulator.
It now can sit in my pickup bed with the hose coiled on top. I can hook it up to the trailer gas outlet or a 20# cylinder at home without having to use a wrench.
I think AS uses 1/4" Quick Disconnect so the set sold by US Carb may not fit. I didn't use the hose that came with the trailer so I kept it for a grill in the future (now I use the Coleman Roadtrip that I connect to a tee fitting from Camco at one of the 40# cylinders). You will need a few odd pieces to get all of the plumbing to fit together. I used the thicker yellow Teflon tape and was super careful to prevent any pieces from getting inside the piping. It's much nicer than getting pipe dope all over your clothes whenever you touch it.
It took a few tries to adjust the max flow nut, but it starts and runs great. I'm very happy with it all around. It's quiet, runs forever, looks good and just barely a 1 man lift into the truck.
Only lesson learned is to make sure everything else (fridge, water heater) is on gas when running the AC to avoid tripping the overload protection.