The advice given by crutschow and Hero is on the money, but for added consideration I will add the following.
First, contact the battery manufacturer of the batteries you will be purchasing to find out the exact type of battery, antimony-acid or lead-acid or whatever, to determine the correct float voltage and charge rate for the battery in the configuration in which you have described. There is a difference in these parameters for the different types, which could result in an over or under charge of the batts, resulting in a shortening of their life, including excessive H2 emissions.
Second, I would strongly recommend bringing aboard a certified marine electrician, to, at the least, review the installation for ventilation, wire ampacity, charge and float rate/voltage, accessibility, installation practice (numerous factors), etc. Fire at sea can be very deadly. Better yet, get someone certified from the start to advise from the start.
Third, insure your charging/float system is stable and monitored periodically.
Forth, establish a regular PM schedule to check batt electrolyte level and specific gravity.
This may seem like overkill, but if you can't get in touch with the Coast Guard because of a fire in the battery compartment and you're dead in the water, you may wish those bases had been covered.