IF the garage temps are to be above freezing, absolutely not -- that's a nifty bonus for being able to get the camper inside for winter storage. Spring will mean a bit quick(er) and easier flush and sanitize. A nice perk!!
I know this is an older thread - just getting caught up in the PUP community after a long winter... We live in central PA and store our PUP in our garage that is semi-heated. (1st floor of our townhouse) Our first year we did winterize but I kept a log of the temperatures in the garage throughout winter and since the temperature never got below 50* we opted to not winterize this year. This winter was much milder for us this year so we are happy with our decision.