I would 2nd that idea of making sure you get metal contact. Just throwing a piece of bonding on painted parts will not effectively do anything, except maybe keep the bonded part from falling off the vehicle.
I had my 857 mounted near the center console. I could easily rest my arm on the top of the center console and tune around. It was comfortable. But I have had lots of experience listening with my father at home when I was younger. I have listened to poor radios with poor antennas and great radios with great antennas and also awesome radios with awesome antennas. I must say, with a beam antenna at 100' pointed anywhere with a well tuned radio and 1500W PEP AMP on your side, it is a nice warm feeling. You only get that with a less equipped station when you make that QSO that should not have been made. A 5-9+20 signal report from Spain at 4:30 in the afternoon traveling through Denver rush hour traffic gets me that warm feeling. Especially barefoot mobile.
Blue '99 UZJ100 2" Lift, Replicated Outback stackable drawer system, Engle 63 QT, Custom Front Bumper, Gamiviti Shorty roofrack.