We used to run 4 group 24s, now have 4 GSs in the same space. Needed some work for the increased headroom requirements. The group 24s lasted three years with some babysitting. They did NOT keep the rated (total) 225 AH for all of that time.
Yes, 3X75=225, and are on the face of it equal to 2 GSs (More or less--some--ours--have higher capacity, up to 242 or so. However, the GSs will handle deeper discharge, ie down to 50%, quite well. I found that the group 24s de-rated pretty fast if not taken up to 100% charge which is difficult without shore power or solar. For part of the time we had 160 watts of solar, the last 2 years we had 420 watts of solar. Most of the time we were able to fully recharge the batteries.
If I were to go the 3 12 volt route I would consider using three group 27s, 29s or 31s depending on price and AH ratings if of course they would fit. I believe the original house batteries in our rig were 3 group 31 Marine/Deep Cycle. They had 2 of those for chassis (starting) batteries and the last set of those, in the rig when I bought it used 5 years ago, were just replaced with the same.
Pianotuna, a regular poster here on this board, recommends using 50 to 160 (I think) watts of solar per 100 AH of battery. We have now 420 watts of solar for 484 AH of battery and would be a bit happier with more solar. Sometimes size matters :B.
Edited for typos this morning when I was more awake. :)
