1st of all, the tow vehicle pictured is does not have near enough tow capacity for that sized trailer.
A lot depends on how cold the temps are going to be and how long you stay whether the extra propane bottle is going to be enough.
If using the Wave Heater, adequate ventilation is a must !!! If you are not camping around other people, an option might be to run the genny 24/7......the genny should keep the battery charged so you can run the furnace instead of having to use the Wave Heater.
Flushing the toilet with antifreeze might work....but will be a little expensive. If you are in an isolated area instead of a campground, making a yellow hole in the snow would be an option instead of peeing in the toilet and diluting the RV antifreeze. You can use the toilet for more important things
, keeping in mind that there needs to be plenty of fluids (in this case RV antifreeze) in the tank to keep the solids from adhering to the tank.
The gray tank would be more of a concern. You would really need to keep the concentration of RV antifreeze high to counteract the water going down the sink and shower drains.
If your trailer has an enclosed underbelly with furnace ducting in that area, that would be another reason to run the furnace instead of the Wave Heater.....it would keep the tanks warmer than the outside air. But I would still want 100% antifreeze in the dump lines, because they would be outside of the heater area. A couple gallons in each tank right off to fill those voids might be necessary.