The headliner was a piece of cake! I removed the drivers side rear grab handle (2 8mm bolts) and the trim work on the rear “C” post (there is a 7 mm screw under the tab) along with the rubber door gasket. That allowed me to drop the headliner done plenty far. I use a pick to pop the covers on the grab handle covers. When I put the 7mm screw back on the trim, I wrap it with a single layer of electrical tape on the socket, so I don’t loose it in the panel. The trim hardware is about identical on all chevys (Tahoe’s, Silverado’s, etc)
I use a 3/4” antenna bit, so I don’t blast through the headliner when I drill.
I ran the cable down the C post under the rear seat where the radio is. All in all, about 30 minutes. I did everything on the drivers side
you can always run the mount and put a weatherproof NMO cap on it, until you use it.