I was thinking of the same thing for my 30DSQB, but instead when with 2x12 volt 24 series. I also carry an extra 12 volt 27 series battery in my truck that I use for tailgating at the lake for some tunes, phone charger, etc. when we aren't near the trailer.
Two things kept from converting.
1. Price. $380 just for the 2 6 volt batteries, compared to $120 battery plus $40 for the hardware to install. Especially since my battery on the trailer is only 3 months old.
2. Now this sounds kind of weird, but I couldn't find a box that would fit the 6 volt batteries, and still fit in the space allowed on the tongue of the trailer. So I would need a custom fit box...which is more $$$ in for the extended battery life.