If you ever want to fish any wires through the tailgate, such as coaxes, rear view camera cabling, etc, etc., you'll be kicking yourself for filling the tailgate with foam.
There's also a vent through the tailgate, which is not really a big deal if you have a soft top, but with a hard top, you'll regret blocking it as it allows the pressure inside the cabin to equalize with the outside.
Before I got carried away with doing something irreversible, I would spend some time trying to isolate exactly what is rattling. Could be a lot of things -- maybe as simple as the plastic cover over the interior wiring. Better to try a scalpel before you pick up the ax.
But if you do end up spraying something, I'd do a coat of bed liner on the interior side of the tailgate and let it damp the vibrations like boom mat, etc., but more functional and better looking.
Having a fawking JL 13W whatever the fuck might be the cause of the rattle, simple solution is to remove it and go back to having shitty bass. Or, stuff rags in there. Or, use a spray on sound deadening solution on the tailgate inner skin and inside surface. Or, fill the tailgate with like four cans of Great Stuff and watch the fucker bulge out like a Jiffy Pop, which i'd prefer to see. :laughing2:
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