Plumbing system winterization - when should I be conerned?

My thought is that if you plan (hope) to use the rig some more, maybe even occasionally during winter, why not learn how to winterize yourself? It only takes a little time (and some money if you use anti-freeze), but is easy to undo should you want to take late fall or mid-winter trips. I winterize my trailer about eight times (or more) a year (have already done it twice now). I choose not to use anti-freeze other than in the traps. Instead, I just blow out the lines and drain everything well.

Have a great winter,
Steve