I use one of these on the roll bar above the passengers head ( I cant remember offhand which size ) with a bolt onto the normal gopro mount
http://www.ebay.co.uk/itm/Marine-Grade-316-Stainless-Steel-P-Clip-Hose-Pipe-Clamp-Cable-Mikalor-Type-Lined-/190900783836?var=&hash=item2c7292cadc:m:mmXEqtx543rMPWv_S7mEBiQ
I dont trust suction cups etc, camera is too expensive !
