RE: Battery Location
As others have pointed out there is room and a place for a starting battery
in the engine compartment, that's where the battery is in the diesels.
As for more convenient access to connect to the battery, the setup Terry Kay
shows on his site would work fine and is easy to make up.  It uses two of
the large Anderson Powerpole connectors, about $10-15 for a pair, plus a
couple of short sections of heavy cable and rings to attach to the battery.
For lighter loads that need 12v just adding additional cigar lighter outlets
in a convenient location should do the trick.
And if all else fails pull that passenger seat and clean up the gummed up
rails :)