TRU SPEC Prefab Single 8" Subwoofer Enclosure Sundown SA
 
 Tru Spec Prefabricated enclosures are simple, straight to the point, subwoofer specific enclosures dialed in precisely to manufacturer's specifications after displacements. These subwoofer specific enclosures will be versatile to many other subwoofers as well, so you do not have to use the noted driver on the enclosure, just be sure and double check your cutout.
TRU SPEC PREFAB SINGLE 8" : Sundown SA-8" with flush baffle
Material: MDF
 
Box External Dimensions
Width × Height × Depth
20.00" × 10.50" × 11.26"
Material Thickness
0.75"
Net Internal Volume
0.65 ft3
Tuning Frequency
35 Hz
Port Area
9.00 inch2
 
Cutout Diameter: 7.45"
Flush Trim Diameter: 9" 
Also fits the following 8" Subwoofers and are close to recommended specifications:
Deaf Bonce Machete MF 8" Subwoofer 
DC Audio M3 8" Subwoofer
CT Sounds Meso 8"
Skar VD 8" 
Skar SDR 8"
Skar SVR 8"
Skar EVL 8"
DS-18 Elite Z 8"
And many more