The water gets in through the windows I have found.Make sure all your windows are sealed,and the door seal is in good nick.The water runs down the fuse inbetween the window and fuse,down behind the trim panels.On to your rear spar attachments.Leaving you in time with rotten rear spars.Not an easy job to fix,but piper do a repair for it.Had an aircraft in the hager a few months back.Brand new wet interior and rotten rear spars.