This is a FYI type post. I recently installed a Cobra 75 in our Class C. I used a battery cable to ground the rear ladder to the frame extensions. I used a 3-way mount to mount the 4 foot Firestik antenna to the ladder with approximately 3 feet above the roof. I ran a 50 foot cable from the antenna up the the dash in front of the driver's seat. I mounted the Cobra 75 interface box under the dash and the all-in-one unit on the dash just to the left of the dog house. I fired it up and got a SWR of 1.7 or less across the CB band. We took a little camping trip into the mountains this past weekend and I got a chance to check it out. The weather bands were present wherever we went. The CB bands seem to have a range 4 to 6 miles with crystal clear communications on both ends. I am happy with the overall performance of the installation. This post may help someone considering doing something similar.
Gary & Mary Hamblen
2006 Gulfstream Ultra LE 6316