Having just been through this I can explain the issues.
Your first problem is fitting the Battle Born batteries. Lead acid GC2 6V batteries are 10.3" long X 7.11" wide and 11.07" high.
The standard Battle Born 100ah battery is 12.76" long × 6.86" wide × 8.95" high. Four of these will not fit in the upper battery tray. You could put them in another location such as the storage area behind the main battery bay. Some folks are installing them under the bed.
However, Battle Born makes a GC2 replacement. It is 10.31" long × 7.28" wide × 11.02" high. Although tight, I think four of these will fit. They are slightly more expensive and sometimes difficult to get.
Your next issue is to separate the Battle Born batteries from the chassis battery and alternator. I would install a Blue Sea ML-ACR. This is a great way to control your house and chassis battery connection and maintain your Boost function. There is another thread on this forum that explains the installation.
Most folks are installing a DC to DC charge controller to protect the alternator. The requirement for this has been debated. If you use the on board generator and inverter to keep your batteries relatively charged you may not need a DC to DC charger. You can read about these in the "Going Green" section.
Your next issue is to keep the Battle Born batteries from freezing as well as from over heating. They make an automatic heating pad to prevent freezing but the high temperature can be a real problem depending on where you live and travel (like the desert southwest).
Now down to the important part. Do you already own this coach?
If not, I would encourage you to research Navistar International. In my opinion just about everything they have touched has been a disaster starting with the class action lawsuit over the Ford Powerstroke engine failures (manufactured by Navistar) and on to the MaxForce diesel engine failures.
Monaco Coach filed bankruptcy in Mar 2009. They were just preparing for 2010 model production. I would recommend staying with a 2002-2009 model Monaco coach. Remember, most 2009 coaches were built in 2008.
Best of luck!