[prairieschooner]

Here is the best way to wire them as a bank


and with four they should be like this


The key here is to have the + and - Cables at opposing ends of the bank, this allow the best use of the Banks. I have had our wired this way for the past 5 years. Congratulations on choosing this option over 8D's as this should give you more usable power. The attachment below is the wrong way to wire them.

Here is a link to a site that helps describe it;
6 volt deep cycle battery connected in series « San Diego RV, Solar, Marine & Golf Cart Battery