Mstern: what happens when you hit GRP with a hammer? Ok now how about wood? Now tell us what light houses are made of. Cement really isn't dumb as a building material and add to the list of benefits easy to repair any where in the world.
Now for the electrical and plumbing on the vast majority of inexpensive fiberglass or any other material boats. Lots done by "handymen". Automotive and household materials.
I'm no ferrobooster but as I understand it, low quality galvanized armature wire was the big problem with many homebuilt ferro hulls. If you can find a surveyor who knows them and it checks out then why not ferro. Cheap does sometimes translate to good value if you're careful.