Don't want to discount the obvious daftness of the question, but it would be possible.
Ambient temperature in the boot would be say 10°C? In the engine bay this would be nearer 80°C. You just need to find an amplifier that can handle the higher ambient temperature. The components inside the amp will have a temperature limit. The temperature rise of these components over the ambient temperature will mostly be directly proportional to the power output of the amp.
So the lower power you are pushing out of the amp then the lower the temperature rise of the components and the more chance you have of siting it in the engine bay.
So if the temperature limit of the components is higher than engine bay ambient temperature then there is a very slight possibility of doing it.
If the temperature limit is less than 80°C then you have no chance.
You could look at installing a water jacket, pump and external cooler if you want to have a go.
But grow up lad stop asking stupid questions!