I lined the engine compartment hatch with 1" foil faced fiber-glass duct board. Creative use of *real* aluminum foil duct tape sealed the edges and reinforces the mastic which fastens it to the 1/4" ply.It works so well that I intend to apply it to the entire compartment....some day
. The compartments bulkheads are plywood; so a few screws with fender washers to keep it in place till the mastic sets is all it will take. Then a contortionists game applying tape to the joints/seams.....
Avail. at most HVAC suppliers and possibly by order at big-box stores?