Thanks, they are a cheap option, also used one behind the electronics in the console. It gave me somewhere to drill and attach stuff with only four bolts sticking through the front of the console.
The Polymetal is extremely quiet, when you drop something on it there is a muted thud. So I highly recommend it to make an aluminum boat quiet. It is light and strong. My lower floor is 1" pink foam between the ribs and polymetal over it, basicly no noise when you drop something on it.
Only thing that I would warn about it is the aluminum is very thin on each side, so you have to be careful drilling the holes to rivet it on, it tears easily when drilling. The 3mm is about $50 for a 4'x8' sheet. Problem is finding it. Best place to check is local sign shops. Mine came from overstock from a friends project at work. They ordered 19 sheets and had 1 left over.