Another NOOB question. Dampening material inside a sub?

Sorry for clogging up your subwoofer section with noob questions🙂

I have a whole load of roof flashing tape.. You know, that bitumen based plastic backed type stuff. I used to used it in place of real car audio damping materials back in my poor young man days. Heat it up with a hair dryer, roll/squish/press it on, and it does a fair job of damping vibrations.

So - the question is this: Is it worth chucking some in my 2x 15 sealed down firing subs I'm making? I believe the box will be ery stiff anyways.... But.. it all adds up right?

Is it worth it?

Thanks,
J James.