Here is a link to Trojan 12v deep cycle batteries.
https://www.trojanbattery.com/markets/mr/12v/
There are several different kinds. I think if you back up to the main page you can find their 6V batteries as well. When replacing keep in mind the physical limitations of the space you have to put them, if any. On mine, 2 group 24 batteries fill the built in bracket to the edges, the extra length of a 27 won't fit. I am also limited by height because the batteries are enclosed back behind a cowl and the LP tanks and have very limited access space. 2 6v might fit but I've not done any in depth research because I just don't need them. We dry camp very seldom.