Are your water lines exposed? If so, heat-taping them may be your only choice.
Since your under-tanks are also exposed, I will guess your lines are exposed.
May not be feasible, except winterize the rig and just sleep in it (although a bucket of water may make the "facility" flushable.
Personally our rig is enclosed and heated and have had no issues in temps into the mid teens, well, other then the supply hose (outside) froze up.
I know of an owner of the same brand (he is here on this forum) that winters over in North Dakota, but he also takes a bunch of extra steps.