Before doing anything to the toilet, I'd call around to the local RV parks, gas stations with dumps and the municipal waste treatment plant and find out if any will let you use their dump station, even if they are "officially" closed.
While many RV parks close Oct / Nov, lock the gate and then disappear for the winter around here. Many over winter comfortably at home. When I've needed water or needed to dump I'll stop by and ask if I can dump and fill with water, even if they are closed for the winter. Most are very empathetic and help out. I don't take change and somehow only have larger bills :). The KOA outside of Revelstoke, BC was very helpful, even though closed. If they can't help out, I simply ask if they know of a place.
A lot of the gas stations have dump stations you can still use as long as they don't bury them, when they plow the lot. Our local conoco station has a dump station accessible year round. A quick call is easier than making your own dump station this time of the year. I dug down to find my septic tank and have it pumped earlier this year. I installed risers and a lid so I won't have to do it again. Pretty simple to add a 4" fitting to the riser lid to make it into a dump station at home.
As to everything being frozen, we run full utilities all year round. While it was -2F this morning, the temperature in the basement near the tanks stays above 45F and inside it is at 70F while on our winter road trips to ski areas in MT, BC and AB. The coldest the inside of the camper gets in the winter, is when it sits on the truck or cart in the 60F heated garage between trips ;)