Just as a point of information - a battery isolator is just two high current diodes with the alt charge wire in the middle. No contacts to wear out or corrode like a switch, and a diode is one of the most basic electrical items used in most EVERYTHING that has electronics - it lets electricity flow one way, but not the other.
IMHO the best setup is two batteries and two electrical systems - one for the foo foo stuff like lights, stereo, coolers, etc - the other for the engine. These two systems powered off of a single alternator / isolator that will automagically charge the two batteries at the same time without affecting the other one. In this "perfect" system you also have a switch or high current relay that is normally in the off position but can be turned on to connect all batteries in an emergency. This is really handy if the engine bat is dead or dies and you need to start the engine (or if both batteries are near dead and that extra uomph will keep you from being a swimmer).
