Well sportsmobile fans this the very device I was seeking.
http://www.perfectswitch.com/dc-solid-s ... al-relays/ This is an incredible little device that goes between the battery bank and inverter/charger. It draws almost no power and allows power to flow both ways for charging as well. It is also fully customizable in terms of up and down thresholds. Wi th the switch I just heat up the water before I leave or while I drive and the very well insulated tank keeps it hot for 12-24 hours. I just need to add a bit more heat with the panels as I use or lose it. That way I can turn on the switch and it will mind voltage for me at camp while I'm off. As a rabid Mtn bike guy having a hot shower is pretty much non-negotiable. As long as there is decent sunshine I will have said water when I get back at dusk. If not, then I have to use the engine. The Isotemp therm? Is plumbed via the engine hot water for that too but I prefer not to start it when I get settled. I will let you all know how it works if anybody cares. And yes, next generation lithium batteries should solve the problem too. I can't wait till they come down in price as well.