Here's some progress pictures of the interior after getting the Dynaliner down and the back wall covered. Along with the large 24" x 70" hard board I also cut and shaped 2 pieces of 16ga to cover the rear corners. I covered the 16ga in the same cloth as the hard board.
I also found a piece of large square foam (grey) that I cut in two and glued it to the hard board inside the corners. Now the corners are "full" and shouldn't have any echo or acoustics emminate from them.
As part of this process I removed the fuel tank from inside the cab since I have never used it (I use the frame mount tank only). I think the tank was also a source of resinating noise (hollow can). I want to keep the filler spout on the outside of the cab (it adds character) so I cut it where it connects to the tank and welded a plate with a nut inside to the end of it. I cut it where it meets the 16ga and drilled a hole for a 1/4" bolt to hold the spout firmly.
Hopefully the pictures will help explain more of what I'm describing.
https://plus.google.com/photos/115050180406101428512/albums/6010462565621295425
