i used the factory rubber gasket with the screws, and for safe measure i used a little 5200 around the outside
agreed. use the blockoff plate with the stock rubber gasket, and screws, then a little 5200 to help seal it up.
the outlet i would use some good stainless screws, and 5200 to install it, if it doesnt have a backing plate. also predrill the holes slightly so the fiberglass doesnt splinter and crack.