In my 12H-T into FJ80 swap I am running an isolated deep cycle battery for my accessories. I've decided to give the Redarc Smartstart a try...and I am very VERY pleased with it. I picked it up from Ebay for around $100, and it arrived in the mail from Australia in about a week.
The way the Smartstart works, it monitors your starting battery's voltage and isolates the deep cycle until the starting battery reaches full charge. Once it hits full charge, the Smartstart connects the deep cycle and both batteries receive charge current from the alternator. Since it gives priority to the starting battery, it shouldn't ever go flat.
BUT...should your starting battery ever go flat for whatever reason, all you need to do is hit a switch on your dashboard and the Smartstart will parallel the two batteries and you can in effect give yourself a boost.
Also, you can mount a status LED on the dash and it will tell you what's going on with the system...including flashing error codes if there's something wrong with the solenoid or either battery. Unlike traditional isolators which are very inefficient as evidenced by their massive heat sinks, the SMartstart is computer controlled and very efficient...the whole unit is tiny and easily installed anywhere.
This system is very popular in Australia...and I can see why. Anyway...that would be my recommendation for a dual battery system.
Stone
Jeff Steiger - 
Linear Mode
