If you have a typical "dumb" inverter/charger, I'd use a disconnect switch, then put a maintainer/tender on the batteries to keep them in tip-top shape. If you leave it plugged-in, it will cook your batteries...ask me how I know :S
If you have a "smart" inverter/charger, then I'd just leave it plugged in and not disconnect the batteries. It will maintain your batteries just as an external maintainer/charger would.
I've used Water Miser caps for two years.
While I check my water levels regularly, I've have never had to add water, the caps don't let the water evaporate to the atmosphere - they capture and re-introduce the water to the cell.
