The wire between the tuner and the antenna is part of the antenna and will radiate RF so it should be routed away from other metal objects. In a marine environment its a good idea to use stranded insulated wire to protect from corrosion and goop the connections with RTV Silicone. Any good outdoor rated insulated wire is fine and #12 would be a god size for up to 1kw. If there is a chance people might come in contact with the wire while your transmitting you can use solid core spark plug wire, just make sure the actual wire is a reasonable size and not something like #30. One thing most people forget is the tuner needs a good counterpoise (ground plane) to work against. If the tuner is located near the water line and there is a very short and direct connection available to a zinc, that may work. Otherwise run several wires along the perimeter of the hull for the length of the hull if possible, you want the most wire under the vertical radiator as possible. If the tuner will not tune and it keeps hunting for a match that's a good sign the counterpoise is not adequate. In this case sometimes changing the length of the counterpoise a few feet can make it happy.
Good luck with your install.
prcguy
