I am not going to suggest a brand.. I will say mine are DEKA G-20's (GC-2 class 6 volt by 230 amp hours make one 12 volt 230 amp hour battery when put in series and then we start paralleling) I had Interstates in the past.. Why did I switch.. What the store carried.. Both are good. Trojan's have a very good rep as well..
Before you do anythign get either two SMALL cans of spray paint (Hobby stores have small cans) or nail polish .. one red and one black.
Now the wires that go from a battery to who knows where (not to another battery) Of the battery terminal is POSITIVE spray or paint 'em red
If Negative black>
Let dry
Take pictures clearly showing hookup
Note 2: Traditionally red is positive in automotive and electronics and black negative but in the wonderful wacky world of RV's. "Tradition" is a word in the dictionary.. For the house is wired by ELECTRICIANS and they use a different color code. Thus paint first. disconnect a day later to let paint dry
And if more than one wire (other than battery to battery jumpers) on a terminal use a twist tie, zip lock or other means to join them so one does not get lost
Start by disconnecting the NEGATIVE than any jumpers lastly the POSITIVE and insulate those (even if all you do is wrap a shop cloth around 'em) just to be safe.. Reconenct in reverse order.