With newer trailers using PEX tubing the chances are nil that you'll have problems from just blowing lines. PEX has the ability to expand. Even if some water is left in a line it will expand in opposite directions. It's not like the whole line is full like your house plumbing and there's no way to expand.
I've been blowing only and have had zero issues. In fact when we bought our 1st TT the dealer offered to show me how to winterize it for $50.00. I asked what they did and they said they just blow the lines. I passed on the lesson.
I do live in Oregon in the valley, so we don't get those really low temps like someone living in North Dakota might. But we do have stretches of a week or so when the temps barely get above freezing during the day and drop to the upper 20's to 32* at night. Certainly low enough to cause problems with freezing pipes if not properly maintained.
