Tfoose,
What you can do is install a auto battery isolator, if you choose one of your engine batteries to be the charge supply battery your engine can charge both, the redarc system is an Australian one (from where i am) and it separates your "house" battery until your initial battery (start) battery is fully charged then applies the feed to the "house battery. All you need to do is connect your accessories to the house battery and leave the main charge lead to the start battery, that way you can completely drain the house battery and still start your engine.
Have a look at the link below for some guidance
http://redarc.com.au/products-and-se...ttery-isolator
BTW - I know they state for 4x4 use but i had this in my Bayliner for 3 years with out fault and it did get wet.
Regards
Huddo
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