We get questions like this every once in a while. Getting 8 inches is not an easy, but let's explore some options.
The Anderson you have at the lowest point sits at 16-3/4 inches and then uses the adapter. You may gain 2 inches by using the Demco Recon Gooseneck-to-5th Wheel Trailer Hitch Adapter - Single Jaw - 21,000 lbs # DM8550045 which has a lowest height at 15-1/2 inches. The more in depth installation of the Ranch Hitch Universal 5th-Wheel-to-Gooseneck Coupler Adapter # AM3100... view full answer...
The Vision S 7 inch monitor has the same reception as the 5 inch monitors so that is an odd problem to have. I would make sure all of the antennas are pointed up if you can on the cameras as that is what typically causes this problem. view full answer...