Very nice setup this guy has. He clearly knows what he's doing. The other, and probably easier and cleaner option appears to be placement of two Odyssey PC1200MJT batteries side-by-side and longways in the stock battery location.
FlyingWil (
http://expeditionportal.com/forum/showthread.php?p=89760&highlight=Dual+batteries#post89760) has this setup in his first generation Tacoma and based on measurements of my 2008 it will fit second generation Tacomas as well. These batteries are remarkably small (7.87"L x 6.66"W x 7.75"H) but are comparable in power to the stock battery. It seems like a simple matter of fabricating a larger battery tray and adding some hold-down components. Add a battery separator and you're all set. I think I'm covered. Thanks, guys!