I don't think there are any springs that are more heavy duty than the ones from Honda for their spoiler. Mounting an amp on the trunk lid is a LOT of extra weight for the trunk. I hear you about not wanting to loose trunk space, but subjecting an amp to the open and closure of the trunk is something I personally would not do. See if your insaller can find a different location for the amp.

 

You have your car back?! Why don't you chat with Larry about it. He might have some ideas.