RE: Outgassing from the battery
I think Dennis has hit the nail on the head here, about the only advantage
I've been able to see to the AGM batteries is no out gassing.  And If you
don't think that your stock battery doesn't give of some corrosive fumes,
look at a Westy with aux battery that hasn't had the vent hose connected dor
a couple of years, look at the back of the driver seat just above the
battery.  Oh yeah, the Optima Yellow Top deep cycle is apparently the on
deep sycle rated battery that will fit (after some manipulation).