Need some suggestions on upgrading batteries for dry camping

Deep cycle lead acid batteries are not sealed. They are not maintenance free.
I would suggest using 6 volt golf cart batteries wired in series. They are about $80 at Costco. You could use four wired in series-parrallel configuration.
I would suggest recharging via genset every couple days. Don't let them get down too far.
Verify that your converter is a multi-stage one.