Yes .... you can gang any number of 12 volt RV batteries together in parallel so long as you have them connected in a balanced manner to get even sharing of current among them when charging from RV charging sources, and even sharing of current among them when discharging into RV loads. A buss bar is not necessary, or even optimum from a pure electrical principles perspective.
What "balanced" means is simple: The total wire length and type from every positive battery terminal to every load or charging source in the RV must be identical, and the total wire length and type from every negative battery terminal to every load or charging source in the RV must be identical. The electrical lingo version of this is: The DC resistance to electrical current flow from every positive battery terminal to evey load or charging source in the RV must be the same value for each battery terminal, and the DC resistance to electrical current flow from every negative battery terminal to every load or charging source in the RV must the same value for each battery terminal.
Method 3 in this link can be used to connect any number of 12 volt RV batteries in parallel so that they are are balanced:
http://www.smartgauge.co.uk/batt_con.htmlEither Method 3 or Method 4 in the link above can be used to connect four(4) 12 volt RV batteries in parallel so that they are balanced.
It's obvious that using Method 3 can provide balance for any number of batteries in parallel. You can see - with some careful study - that Method 4 provides balance for four(4) batteries in parallel. Probably the Method 4 approach could also be used for any number of batteries in parallel too ... but you would have to carefully diagram this out so as to keep all total wire and type lengths identical for balance.
It depends upon individual situations whether the Method 3, or Method 4 connection method would be "simpler".
