Remove all water from lines. There are 2 ways generally used, and folks here will argue forever about which is best.
1. open low point drain lines and drain all water you can. Close the drains and hook a low pressure, high volume air compressor to the shore water inlet and blow out the rest of the water. Be sure you get ALL faucets, showers, ice makers, toilets, etc.
I have a friend who bought a 5er and didn't ask me how to winterize. He just opened the low point drains and called it good. He was lucky. He only had to replace the plumbing in his shower compartment.
2. use your water pump to pump the pink antifreeze through all of the same lines. Usually takes about 2 gallons to do this.
ADDENDUM: with both methods, you need to drain the water heater and fresh water tank, and pour the pink antifreeze into the sink and shower traps, and into the toilet bowl.