Hi, Jamie - top piece just lays there, I'm using staples into the plywood on the verticle pieces. I'm using Dynamat sealing tape between the pieces - staples go thru the tape first, as they will pull thru the MLV .
Weight is 1lb per square foot - suspect I used about 50 sqft. That is why luxury cars weigh so much.....if you look at a good OEM dash mat there is a lot of mass there!
__________________
|