It's hardly an all day project and it's always better to do it the right way the first time. I've installed my share of ports and below the water line thru hulls in foam and balsa cored hulls and it's just too easy to do it right.

I would not install a port without any fasteners I use at least two, one at the front and back on center line. Strange things can happen during a capsize. The last thing you want is that port to leave the boat while on it's side.