In 09 or 08. We traveled back from Florida in low twenty degree weather. About 600 miles. We didn't have any problems with freezing tanks.
I am no expert but it would seem, in order, to have a small heater or a heat tape on the pipes in the wet bay. Of course run the generator.
I don't think we have a 120 plug in the wet bay but there is twelve volt but it would over load the circuit for the bay lights. There is 120 on the bay opposite the wet bay on ours so it might not be at all difficult to wire there. A ground fault plug of course.
Another idea is if you have heated tanks or if you didn't a heat pad might be available in the size or altered to fit the three pipes in the wet bay.
Someone here has done something about it I'm sure. I don't hear a lot about cold weather packages on Motorhomes but some do have them. Apparently yours does. Check what they might have done already in the wet bay. Another thing we have at least one drain hole about half an inch in case water get in there. Put a piece of tape over it to keep out some colder air.