Joe,
I am sorry but you have perhaps unintentionally been economical with the facts. My research informs me that your Imala is probably fitted with Sargent electrical distribution systems. I have extracted the appropriate diagram from the manual and attached it below. As you should be aware you need to connect to fused starter, and habitation batteries. Sargent are consistent with their wiring colours, with brown/green (NG) being the vehicle or starter battery, and brown/blue (NU) being the habitation battery, and white/orange (WO) being earth. The only places where these circuits are presented together are at the EC176 PSU, which has plug in connections, and at the Solar option if fitted. If the solar option is fitted and connects with the starter battery, then why do you need a battery master? However the solar option unit shown above the regulator may be the best option for making tidy connections to a battery master. I am wondering whether if you do not have the solar option fitted, provision may have been made for it in the wiring? If so, then you should be exploring a suitable location in the immediate vicinity.