Dead Nuts On (DNO) is a Mustang reproduction parts manufacturer and retailer who doesn't sell pre-cut Camaro trunk underlayment panels (the DNO catalogue post above at $240 is for a '69 Mustang). They do however sell the underlayment product in bulk and you'll need 3 linear feet of it to make a Gen 1 Camaro trunk underlayment panel. To place an order you'll have to call them, you can't buy bulk material on-line through their web site and it will cost about $80 + shipping. On my build thread
Page 31, Post 606 (link:
https://www.camaros.net/threads/1969...ost-1783361132) there is a description and photos of how I made the panel in the photo above (Post #2). I used the same bulk material from DNO to make the interior compartment floor underlayment as well
Page 44, Post 878 . DNO produces underlayment material once a year usually in the spring because the ambient temperature needs to be high enough for the sandwiched asphalt to flow, chances are they have or will have inventory. As aside you stated in your first post
"... paper sound deadener over the muffler area on deluxe interior cars early build with chamber exhaust". The trunk underlayment panel was factory installed on 68 and 69 Camaros with Deluxe Interior regardless of build date or exhaust configuration. According to John Hinkley it was installed to reduce harmonic noise transfer from the differential. The Deluxe Interior option also added additional underlayment panels on the interior floor. Hope that helps