I am sure you know this but anything on Ebay, even if its not "best offer", offer to pay a lower price. Its worked for me a few times.
These covers are easy to spray paint and I did not use high heat paint on mine.

 

I apologize if this has already been discussed but when you were tracking engine air temps with/without the cover under various operating conditions, was air temp inside the intake measured?

 

The figures quoted are all IAT (Intake air temp)

When I was locating the hot spots under the bonnet I was using a dual probe thermocouple placed at various points around the engine bay.

I did measure the both sides of the engine cover and found quite a drop in temp.
I did not publish the thermocouple temps and and see if I can find them if you need them.
The space over the engine bay cover would easily go over 150degC at idle while the air around the exhaust manifolds (probe not on the metal) were around 300c.
This would drop off to ambient for both above 45kph

The Delay under the cover was substantial. Temps did not seem to rise till you had a 50degc+ difference
However as the temp rises quickly at idle this is not a true value. The longer the car was at idle the hotter the temp gets over the cover and the more heat penetrates
A more accurate figure is when the temp outside the cover was 150c under the cover rise from ambient to 50c
The difference when running the fans was the under bonnet temps kept to approx 30c (max) above ambient with no effect under the cover
As this cool air is blowing over the radiator (engine and s/c) I could keep the IAT at ambient and the S/C coolant temps low giving the best results on the track

Just on another note. I did not test the air temps at either end of the intake tube for 2 reasons.
First the issue is with the heat at the exhaust manifold so there was no point once that was found
Second my intake is already ceramic coated and would have little difference.
You really need to test OEM (plastic) over the stainless tube uncoated

I think I said this before but the primary reason for coating my tube was to get a stock look and I did this before I fitted the tube.
The ceramic coating helps with heat soak but again the real issue is the exhaust.

Coating the tube is shutting the gate after the horse has bolted.
If you ceramic coat the exhaust manifold, problem solved and at that point the engine cover will have little effect as you have removed the heat source

Cheers
34by151