I had a 197 like yours. I put a second battery, along with the first, in a nice PLANO tool box and mounted it where the old battery box sat. I even vented it with a couple of plastic plumbing elbows. Worked like a charm.
I traded the 2008 for a 2012 with a pull out, let the batteries go with the 2008. In my amazing brilliance, I bought two nice BIG deep cycle batteries that were on sale. Crap! They wouldn't fit in the PLANO box. I needed the trailer to be operational so I built a wooden box to hold the batteries, at least until I can find a factory box. The 2012 197 has two 20 lb. tanks.
I also have two good batteries in my old Suburban, one with a cutout. I am not sure what people are doing to wear down batteries, but I know I can last for a while.