From doing a google image search here . . . i may be wrong, but it looks like he uses Conklin basses?
on a quick scower of the conklin site: http://www.conklinguitars.com/artistprofile.html hope that helps (yeah, he's in there)
Conklin. Both Custom instruments and his signature Groove Tools 7. Accugroove cabinets, too, if I remember correctly. Important part of his sound nonetheless.