On my brand new 390MB the dealer measured carefully and cut the pilot hole from the inside then went outside and used a hole saw, while I cried.
All was redeemed when he put on the chrome vent!
2017 GMC 3500HD Denali DRW pulling a
2018 RW3901MB, Disc Brakes, Dual ACs, Auto Sat Dish,
Stack W/D, 5500 Onan, Andersen Ultimate Hitch, 400 Watts of Solar fun!