The 240v and 12v elements can be fitted together, to give you a three-way fridge, but not enough room in the tube to fit both. You can get round this by attaching one of the elements to the outside of the tube with jubilee clips. One idea that I always wanted to try was to run a feed and return from the engine cooling system to a fine bore copper coil wrapped around the heater element tube so it would work with the engine running and hopefully keep things cool while driving.
