I think I know the answer, but thought I'd ask anyway.
I've winterized our U300 with the 6V92TA engine. I have a full tank of diesel. Unless we get an Associate Pastor/Head Teacher in January or so, the next time I expect to start the engines will be after school is done in May. If I wait until then, I shouldn't need any anti-gel treatment, as all danger of frost should be past. IF the new guy comes in January, we'd like to leave about a month or so after he arrives, just to make the transition easier. Of course, temperatures will be rather chilly then...
My thought is that I ought to pick up a bottle and dump in it now. Temps are fluctuating about 40* from high to low, so I would think that the stuff will work through the fuel by itself without having to run the engines.
What do the experts think?
Given that you don't know what the temperature will be when you NEED to start it, absolutely, add an anti-gel. Then run the generator and drive the coach long enough/far enough to get the treated fuel circulated AND to get the oil up to temperature.
Then put her to bed for the fall/winter.