Been on the 'net for quite a few years now...and ALL CAPS has always meant yelling or screaming....a kind of internet courtesy thing.
OP doesn't say what his RV is. Presumabably he has looked at the batteries already in there. If it is a gasser like mine, (2001 Ford 5-53) he would need 3 batteries. A 12V for the starter (or motor) and 2 6V (in series) for the coach.
Brands? Really doesn't matter with my experiences over the years. Sams Club has been DEKA...and good prices, or you can buy the expensive "name" brands like EXIDE or INTERSTATE...no matter. Whatever I use, I get no more than 3-4 years out of them. So...I go for the bucks. Sams or Wal-mart usually.
Series 27 for the 12V....and GC-2 (2 of them) for the 6V.