Complete newbies to making anything from composite materials so just after the most basic information and material recommendations if possible.

We're looking to make a seat base for a bike we're modifying using fibreglass/composite and would like some assistance choosing the materials and gels, resins etc.

I realise we'll need a release agent or wax but to make a strong seat base that we could drill and mount to the frame, what sheet material would be best and with what resin?  It will never been seen so we're not interested in the finish per se rather the strength.

I've seen a video where some wraps or lays plastic sheeting over the area to be glassed over and then just lays the sheet material over the top; is there a particular type of resin which is best for this and won't attack the polythene sheeting.

Apologies for the rather woolly information but like I say, this is an entirely new venture.

Thanks, Ed