I was wondering if I can put Dynamat inside a sub box or a fiberglass box would it just dampen the sound that the subs produce or would it make the subs louder

 

i think it would be pointless unless something is rattling.

 

Unless the sub box is made of plastic........then no.
That's why their made out of thick *** wood...
hence, making them heavy as heck...

 

ya dont put it inside of the box....

now if your box is just leaking.... then get some fiberglass resin and coat the whole inside... it will seal up any leaks...

other than that dynomat should only be on the car....