My experience with any type of stuffing on a ported or vented box is closer to Dukes. It isn't always about the slight changes in effective cabinet volume as much as it is the dampening effect and the amount of output or cancellation because of wave front cancellation inside the box. On a ported box, I personally like 1.5 to 2 inches of unfaced fiberglass glued to the paralleled walls. It does a great job. Some of the foam type products mentioned do a very good job for dampening also, but be aware the more dense or hard the surface is, things start to change from effectively enlarging the box to effectively making the volume less.
Good luck with all of this.
Tim
Good luck with all of this.
Tim