Make sure your snake is on heat for at least 2 weeks after the last feeding to allow for the complete digestion of anything that may be left over in its GI track. Any leftover food can rot in its gut and injure or kill the snake while it is in brumation.
Basically the goal is to reproduce what the snake would feel in the wild. You want to gradually lower the temps to about 60°F. At this temp, a brumating snake will lose very little weight. I typically brumate at 55°F for 2.5-3 months, and my snakes loose less than 1% of their body weight. I have heard of people keeping them in the dark during this time, but I don't, they just get the 10 hr winter light cycles from the sun coming in the window.
Make sure they have a tight hide and clean water during brumation.
Sometimes if my snakes go off of food early I offer them live, smaller prey items to try to intice them to eat a little while longer to I can brumate them when it is actually cold.
If you can't get it to feed anymore this year, remember that basements are a little cooler than the rest of the house, and the floor level is the coolest place in a room.
I hope this helps.
Good luck,
Tom Anderson