I don't have to winterize down here, but whenever I am securing the trailer (getting ready to tow it to the campground or back to storage lot), I always systematically go through a startup/shutdown procedure that involves disconnecting each breaker. The only reason for this is to ensure that I don't inadvertently energize all circuits at once when turning on shore power.
Upon returning to storage I disconnect the main D.C. power switch to the battery to avoid any parasitic power draw.