I'll go out on limb here and say you are thinking too complicated. If you install PEX, winterizing means only draining and then leaving all valves open. In order to do that you need to keep the long runs of pipe either flat on the floor or descending toward the drain valve. You don't need any one-way valves, unless you experience your cold water running backwards due to a compressed air bubble in the water heater (which can often force warm water into the cold pipes).
One item you should consider is a 100 psi relieve valve. This is for expansion as the water heater warms up. It will drip out a couple of ounces if you get to that pressure. This item was installed in all the 70s models I've seen, and is about the size of your thumb. If you have an accumulator on your pump you probably won't need this. BTW, I no longer install pressure regulators. If you think you need one, get one of the external types on your hose that has a built-in gauge and filter.
I always install a cutoff in the line to the toilet. The toilet is the most sensitive plumbing item for freezing. If you break the valve, you can continue using the trailer if you have that cutoff valve. I use a 1/2" ball valve. I sometimes install a cutoff on the hot side of the water heater. IF you get in a condition where you want to drain the system, but need to retain the 6 gallons in the water heater, that valve comes in handy. It also will be handy if you have a leak on you hot side and still need to keep water available on the cold side.
One other feature I recommend is a "standpipe" near the toilet, with a 1/2" ball valve cutoff, a hose bib fitting, and brass cap (the cap is just a backup for the valve, if you ever bump the handle). This will allow you to connect a short hose and rise out the black tank through the throat of the toilet. This beats having to drag a long hose in through the door.