The biggest problem and easiest to remedy is the outdoor shower. Disconnect the shower head and drain it and the hose. The Macerator suggestion is excellent, needs some RV antifreeze in there.
A caution when you do winterize also is the kitchen sprayer. Disconnect and drain it.
Leaving sink cabinets open to get heat from rig is also an excellent suggestion.
Things don't freeze all that fast on cold nights.
Or do what I do, just go to Mexico for the whole winter. We really got cold last night, all the way down to 57oF.