as you can see putting card board would be a death wish.
JEGS 'Quiet Ride' Ultra Sound Deadening / Heat Barrier Kits - JEGS
Try this on your hood and inner fenders.... tap and drill sheet metal pieces to the bottom of your subframe to close it all off....
JEGS Ultra Hi-Temp Exhaust Wrap - JEGS
use that to wrap around your engine block head and oil pan to keep all that heat in even more so...