There won't be 12V at at that particular vent. You can however pull 12V from a nearby ceiling light. You will have to do some snaking around to get the power there, but that's the best place. Make sure it isn't a switched light if possible.
Only the bathroom vent has 12V there, for the pancake fan in that vent already.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR