look up XS power batteries. don't bother with that die hard crap.
2 of those will be more than enough. dont' even bother with isolating them either. one H/O alternator and 2 of those batteries will be WAY more than enough.
the whole isolated battery thing is good in theory, but will be more work than you think. only way to make it really work is to have 2 alternators and 2 batteries where one alt/battery is only for whatever you want to isolate. but then you will be limiting its potential and may create more headaches.
do my set up, and if you NEED to use stuff with the vehicle off, you'll be okay for a little bit. but that kind of drain is what will kill batteries.