Winterizing a Trailer Procedure

Drain all the tanks. Bypass the water heater and drain it, which also gives you an opportunity to check the anode rod. Blow out the lines, or pump RV (pink, non-toxic) antifreeze through them, opening everything (faucets, showers, toilet) until it comes out pink. There's often an open line ahead of the pump for that which you can stick into a bottle of antifreeze (close the valve to the fresh tank, open the valve for the hose). Pour some antifreeze down each drain.

If you don't have solar, or won't be plugged in, take the battery home and charge it one or twice during the winter.

I'm sure there are guides, including video if that floats your boat. Google is your friend.