Yes, two 6V’s in the taller battery boxes just fit on the tongue rack. Little room to spare, enough to take tops off and check fluid levels in batteries. As to why 2 6V golf cart batteries vs 2 12V multi purpose marine deep cycle batteries, it’s all about the usable ampere hours. Golf cart batteries are purpose built (without going into the physics of it) and as it turns out, the exact same purpose you need for energy on your trailer. Multi purpose batteries, even deep cycle have to have the capacity for a large surge for cranking a motor. I was originally going to stay 12V when I decided to upgrade from the original battery, but after lots of research especially on this forum, I was convinced to go 2 6V golf cart batteries from Costco. Awesome setup and inexpensive.