I have done a good bit of boat camping and most often used a French press which makes a nice brew fast. All you need is hot water and your camp stove can heat water pretty fast. Handy dandy themos should keep your brew hot so you can take it with on the water. Throw in a couple LED lanterns and you should not need an inverter or extra battery. Those do work well, but cost quite a bit and once you drain your main battery it will take quite awhile to recharge from your alternator.