I use a "Kontrol Streamline Moisture Trap" as can be found on Am*z*n for less than 4 quid. It's a shallow tray that fits under my back seat. It comes with a decent supply of dessicant which you put in top of tray. As moisture is attracted onto it it dissolves into the bottom reservoir which you empty from time to time (there's a little corner spout so you can simply tip it without taking it apart). The dessicant supplied is enough for several refills (you need to seal the bag of course) but after that you can buy a big tub of "Kilrok" dessicant from your local DIY store very cheaply. The Kontrol trap is the one to go for as it's low level and stable - never had a spillage even in tight turns......