You will want to start by removing all the paint. Anything you stick to the paint will depend upon the adhesion of the paint to the fiberglass, which may not be 100% over the long term. Gluing the veneer to the paint-free deckhouse will likely best be done with an epoxy. The standard contact cement used with veneers will be too vulnerable to moisture in a deckhouse situation. After gluing the veneer to the deckhouse and then covering the exposed surfaces (especially the edges) with epoxy to preclude ANY water from getting near the teak, you will need to varnish the teak with as many coats as you possibly can. UV from the sun will cause the epoxy to turn dark brown, to the point you won''t be able to see the wood underneath it at all, unless varnish is used to protect the epoxy from the UV rays. (This is why cold-molded boat hulls usually end up painted. Keeping up with varnishing all the topsides all the time gets to be quite a chore.) The deckhouse should look nice when you''re done, though matching the grains of the veneers can be tricky.