I've parted with a fair lump of cash to get a Cel-Fi signal booster which will work across my boat, my ute, and the camper. I bought the "Truckers edge" kit, which consists of the Cel-fi booster, Blackhawk bar-mounted aerial, and little paddle aerial for re-transmit. For the boat, I added a 2.4m ZCG aerial on swivel base, and another paddle aerial. The camper gets a panel re-tranmitter, which has a larger re-transmit radius, and will get it's signal from the large yagi aerial I already had, used when you are setting up in the same place for a while. So the idea is I only have to unscrew the aerial plugs and unplug the power when moving from car/boat/camper.
I haven't had a chance to try it on the boat yet, but trips down to Perth through a lot of stretches of generally poor reception show 5 bars on the phone almost continously, so that's a win. On the boat, I need reception up to around 50 nm from the nearest tower, across water for the biggest trip I currently do.. Others report you can get enough reception at this place to be useful.
Anyone else using them on the water?