We need to replace the coach batteries on our Forest River Sunseeker 3010DS motorhome. We currently have (2) deep cycle batteries under our entrance steps. I am considering replacing them with 6 volt instead of 12 volt to gain some storage capacity. I was wondering if anyone knows how many 6 volts will fit under the stairs? The measurements of the 6 volt seem to be taller than 12 volt batteries. Also, any recommendations on brands, 6 vs. 12, etc.