We use the original product of Hardura to insulate the the underside  of the bonnet.  Most think this is a sound deadening product. We know it is used as a protectant. In the case of an engine fire you want to not only protect the bonnet paint but the sheet metal as well.  This product is also thick enough to keep engine heat from causing the adhesive to let go and down comes the insulation. You folks with louvers, you cut your own louver areas.