Buy a 12v kettle... Prices range from £16.00p to £50.00p. Dont overfill it they take ages to boil when full.
Try not to use your ciggy lighter socket for your kettle, The plug gets very hot. Cut the plug off and wire directly to your battery, strong textBig TIP. It will eat the juice from your battery and flatten it if you brew up to many times with out runnin the engine.
Better still wire it directly to your auxillary battery. On the transit if you have two batteries under your drivers seat, its the front battery. The one nearest to the steering wheel.
Auxillaries on a sprinter, Tough. youll have to buy the gear and plumb it in. Thats abt £50 plus batteries if you do it yourself.
And well worth it if you have a TV, DVD, Sat reciever and of course a kettle all for those long journeys or over night stops.