Batboard

Any one done a roof mount antenna on the new body style crew cab Silverado?
I'm looking for any tips on which direction to route the coax from the antenna to the floor.

Thanks

Is it a 2 layered roof? Most of the trucks I've been doing are 1 layer with a support in the middle. Depending on what else is on the roof, I drill towards the rear and run the cables down the back corner and under the carpet/mat to the radio. There may be access in the front windshield posts but it is usually easier to find it in the back.