Don’t cover the whole panel with dynamat. Do little rectangles in the middle 50% of each panel, covering 25% of the panel. Do not link the panels together with dynamat, or you will create a new resonant frequency that your whole trunk vibrates with. That part shouldn’t be too expensive, especially if you get an off-brand.

Then you cover over that with a layer of mass loaded vinyl backed by closed cell foam.

The dynamat dampens vibration. The MLV “blocks” a bit of sound, it’s doing the hard work. The closed cell foam isolates the MLV from the body.

MLV is super expensive, but Home Depot has a cheaper product that works.