twadem...first of all- Welcome to iRV2!!
We are usually a bit faster to answer -so I apologize for not answering last night.
Can you tell us what the normal temps are for the time you will be in NM for the time you are going? You may not need to do anything...
Some things you can do is to do as you asked..and fill your water tank and then use your water pump. You can also put a temp. monitor in your wet bay to monitor the temps. It may stay warm enough that you won't need to do anything else. You can always put a shop drop light in the wet bay and turn the bulb on at night when the temps dip down too.
That is just one idea... I am sure others will tell us what they think...
Again..welcome to iRV2...we hope you visit and post often!