what type truck is it? we usually just pop the 3rd brake light, drill the hole, then pull the coax thru. then feed it along the edge of the headliner to the side trim. no need to drop the liner at all to do this.
if you want it more center of the roof, drill the hole, then use an antenna rod. just tape the coax to the rod, insert it in the hole and work it over to the side. pull the weatherstripping, and grab the rod and pull the coax thru.
CAUTION, if you drill inside one of the double wall frames you may not get the coax out! you then have to drop the liner, drill the support member and pull it. that or plug the hole and start over.