That online shop does another version of the "silent 40" its a thicker one intended for use on military vehicles and trucks apparently so that might be better. I just saved one item from his shop in the myebay list so I knew where to go.
On the other hand, the Gold stuff gets a good review online and it's a bit thicker, they also do a 10mm one
I plan to line the floor with cheap stuff, 2.5mm sheets of closed cell foam just to hide rust, welds etc and then paste the heavy stuff over the top