I've used 5200, lifeseal and GE II, and prefer the GE II in almond. It holds up better, the color matches Grady gelcoat almost perfectly, and silicone is what the plate makers recommend. Especially with the lifeseal, I've had the adhesive caulks come unsealed and let water drain down onto the tanks. I use electrical tape to outline the deck recess, then use a liberal dose of the silicone on the plate. Once screwed into place, I use a finger to make a nice fillet between the edge of the deck plate and the lip of the deck around the plate. If the silicone bead eventually separates from the plate you can easily see it and then reseal. If you keep the silicone only directly under the plate, you can't tell as easily when the seal is compromised. The almond GE II looks great when the deck plate is also almond/gelcoat colored.
