You should search the forums here as this is always discussed. 6 volt deep cycle were designed for heavy usage and deep discharges. This is why they are used on golf carts, fork lifts, large diesel trucks and boat motors etc. The plates and cells are bigger which is why they take longer to discharge vs 12 volts.
Real World: I bought two trojans T125's in 2004. Sold my TT in 2015 still going strong. bought two new t125's and they are on the new to us TT. We dry camp as much as wet camp. 2016 put 428 watts solar on and we dont even bring the generator with us anymore. The heavy duty batts plus solar = works for us. So its more $$ but divided by 10-12years = a good cost benefit not to mention peace of mind while out in the boonies.
happy trails