Polar Vortex in September? How much RV antifreeze?

I just bought our 97 Allegro bus 32' in April and finally had it DEwinterized in June (my mother passed so the bus is just set up in the yard plugged in this year) and I haven't used the water system at all since we brought it home from the service appt. (I received a call from hospice while at the appt. that mother had taken a turn for the worse so we had to run out of there after the work was completed and I didn't really get a lot of information.)

I just made an appt. to have it winterized on Oct. 7th but this morning I hear they are predicting harsh weather as early as September for the Great Lakes so I'm wondering if I should stock up on some RV antifreeze now just in case it gets cold before the appt?

How much do I need and where do you put it other than down sinks and toilet?

I grew up in the north valley of Northern California so my folks didn't have to deal with much winterization.

Thanks.