installing side mount rod holders

howya doin lads. im buying my first boat tomorrow , and i was passing by a marine parts store earlier and picked up a couple of side mount holders. the mount itself is plastic , and the boat im getting is double skinned fibreglass. ive never in my life drilled into fibreglass so my question is how do i go about it . do i just screw in as normal ? do i add rubber or metal between the mount and the side of the boat ? shud i try drill through and out the otherside and fix them that way or is it a type of rawl plug situation ?
basically , help needed lol

pictures or a link to the rod holders might help.

Yep! If you are not sure, pictures before you drill anything!
You might find that rail mount or suchlike might be better....

its all good in the hood ! i fitted them earlier , drilled through with ducktape around the area . just wanted to ask here first