As long as they are "TRUE deep cycle" there seems to be little difference anymore. 6 volt seem to still carry more weight and the lead in the battery is what give the # of amp hours. $$ wise T105's, Trojan batteries still are what others a measured by, Amp hours to cost, and will last IF taken care of. But for the cost one can get 4 of the Costco or Sams club batteries and have more Amp hours than the T-105's . Just look on the batteries and if they have cranking amps "they are not true deep cycle". As to how much battery you need only you know you camping style. If you use hookups a lot then less battery and inverse if you boondock a lot then more battery storage power.
I run 4 T-105's in the HM and do quite a bit of boondocking and would like 2 more but am out of room.
In my sons last TH, he ran 6 cheaper deep cycles and seemed to do fine, but did boondock at the dunes alot.
LEN