Tuning the strings down is a good idea, in my opinion. It lessens the tension, which means your strings are less likely to break. No matter what you do, you’re bound to have to spend a few days re-tuning and re-stretching the strings to adjust for weather differences. When my boyfriend moved my harp from GA to AZ, the humidity (or lack there of) really affected the harp. I spent a good three weeks re-stringing and tuning. Just be warned that you’re going to run into problems with that.
Also, make sure you have a case for it (stating the obvious). Hard cases are generally better if moving to or from a humid place, and they’re better at protecting your harp from damage. Most movers have it in their contract that they cannot be held responsible for any damage done to musical instruments.. This just means that you have to be three times as careful on how you pack it.
Best of luck with the move! 🙂