a Phenolic material like PTFE works best at insulating the manifold from the hot end, especially on track or in traffic, (perhaps also with stainless bolts to further reduce conduction) but 4 stacks of gaskets is better than 1 eh.
even after a track blast, my manifold with spacer is always stone cold
I have a very raised rear bonnet and it's surprising how much hot air flows out of it.
at high speed, I've not tested what the airflows doing considering the high pressure through grills and low pressure going underneath (I'll need to stick some wool along the raised bonnet soon).
but when stationary after a hot run or in traffic, alot of heat builds up very rapidly in that engine bay and having an open top is better than trapping it all in.
the opening at the bonnet rear may not be best sue to higher pressure as skymera says but the front top side of the bonnet may have a lower pressure (after the air strikes the blunt frontal face and goes up over the bonnet curve).
like those cosworth front bonnet vents