Arunas, I opted to use the Gam antenna. I hated the idea of cutting my backstay. Also, a number of my friends have used their backstays, and had a corrosion problem which affected the performance of the antenna. And if you figure in the cost of the insulators and the rigging cost, there really isn't much of a difference in price. Best part of installation of the Gam, as long as you don't have a split backstay, it is easy to install the antenna by yourself at the dock. You just slide it up the backstay and use zip ties ever 5 or 6 feet. Because the antenna is sealed in plastic, no need to shove it up 7 feet above the deck to protect from RF burns. According the Gordon West, it actualy works better with a low angle, so I anchored the bottom to the stem on my turnbuckle.
How does it work?? I've found the Gam is just as effective if not slightly better then an insulated backstay. I've had good signal reports into Japan and Central Mexico from my dock in Southern California, even with not the greatest band conditions that we have right now.
As for a groundplane, I took my general ticket class with Gordon West. He recommended using a thru-hull, using the same thru-hull for both the tuner and transceiver. Just make sure the thru-hull is always in the water. Try it first, as it is the easiest to do. If it doesn't work for you, you can always try the next hardest way and that is running copper foil every where. Last is the dynaplate.