Overall your diagram looks fine. I would add 2 more tee's and a ball valve where I drew it below in red. This will let you bypass the water heater when winterizing the trailer.
You should also add low point drains. One for the hot water line and one for the cold water line. These should be installed at the lowest point of each line, and then make sure each line never goes up and then back down. Additional low places in the lines will trap water when it's time to winterize.
I'm not sure the ball valve on the city water inlet is really needed. If you buy a city water inlet with a built in check valve, then that ball valve would be redundant. Doesn't hurt anything to have it though.
One other point is I did not install shut-off valves at each fixture. Some folks do, some don't. Mostly a personal preference, so install them if you want. Again, they won't hurt and can provide some peace of mind.