[DebNJim B]

We winter south in our camper so store in the summer, usually don't have to winterize. Once In a while we will go home for Christmas and leave the rig, so I blow out the lines. Always be sure to add antifreeze to the traps and toilet.
I read a thread once where someone would add the antifreeze and then blow out the pipes leaving the antifreeze to protect the traps. I would recommend this process and then "winterize" with Clorox solution in the spring to sanitize.
BTW, always drain the H/W tank and it's a good time to inspect/replace the anode.