[DanEC]

I suspect you are focussed on the right area. When assembling my sheet metal I noticed the trunk floor aluminum was prone to tin canning and some noise. I put several strips of adhesive weatherstrip on the bottom side hoping it would brace off the top of the fuel tank but I didn't notice much improvement. I have a carpet kit for mine so I'm also going to put down a layer of B-Quiet 40 mil sound deadner before the carpet and hope that will take care of it.

I think some weatherstripping pieces on the bottom side would still do the trick but I apparently didn't use thick enough weatherstripping to sandwhich it solidly between the tank and floor (I think I used 3/8 inch).