Where can I find this battery? 

I think its AGM - and will fit under the front seats. Since you can't mix AGM with flooded when using a charge controller - I'm going to have to switch all my batteries to AGM - and with no ECU under the rear seat, I can put each of two D31M on either ends, so the weight is evenly distributed (they weigh 60 lbs) - and of course if I get two more of the "000 915 105 CE" then with them under the front seats, they'll be evenly distributed weight as well, even balancing some of the weight under the rear seats. 

Then if I can get an external regulator and bring the voltage up from 13.8 to 14.2, it should be better for charging the AGM (I think), and I can use a battery selector switch with AFD (Bluesea) so if someone inadvertently turns the selector to "Off" the diodes on the alternator wont be ruined from the increase in voltage. 

Does anyone have any experience with these? (they're AGM):
http://www.sunxtender.com/xtenderservice.php