The authoritys in the USA have taken drastic action to enforce the regulations about ferry tanks because these have become popular with drug smuggerlers , and to be caught with an unauthorised ferry tank in the USA puts you in the frame as a suspect drug smuggerler , so dont even think about flying without a permit for such equipment.
The best place to break into the PA32 fuel system is FWD of the main spar in the center section you might even find that you have AN spec "T" unions already fitted ( and blanked off ) if the aircraft was ferryed to europe.