I wish it weren't it metric:thumbsdn:
If you work from Zilch's baffle layout, the outside dimensions are 8" x 14" so you'd get 6.5" x 12.5" internal with 3/4" material. That would need about 8 1/16" of internal depth to get the .38 ft^3 volume. External would be 8" W x 14"H x 9 9/16" D using 3/4" material all around.
Guess I didn't recall so well with that 10".