If you have already drained the lines via the low point drains then your 75% there. If you have access to an air compressor you can blow out the lines to make sure all remaining water in any low spots is gone.
Adjust the output pressure to about 20-30 psi.
Remove the hot water heater plug & drain that.
Go inside & open all the faucets. (Leave open)
Faucets will freeze & the seats will distort & once thawed will leak.
By opening the faucet you leave room for expansion of the internal parts.
I use my 5er right to the end of Dec.
I do the above after each trip from Oct to Dec.
Have never had a problem in 20 years.
Dave, Judy & Daisy May
2010 Sierra 356RL
2011 Silverado 2500 4WD, LT, Ext Cab, LB
Duramax 6.6L V8 Turbo Diesel
Allison 1000 6-Speed Automatic Transmission