Some builders will put damping material on all the interior walls. Make sure the walls near the woofer are heavily covered. In addition to absorbing reflections, damping material can be used to increase the effective cubic volume of the speaker enclosure. Don't compress the material. For adjustment of how much to material to use, judge by your ear.
Fiber glass is the most widely used material.
Acoustical grade fiber glass can be bought for this purpose. You can also substitute other materials such as polyester batting, rug underlayment, even old rags. Don't use dense materials that would significantly change the enclosure volume. The edge of the wood at the edge of the driver will diffract the sound waves. Front mounting permits a more vibration-proof box because there is no need for a removable panel.