Good lord... what have I done?!
Suffice it to say I'm totally out of control with Google Sketchup. I'm not done yet and not really happy with the braces, so this is definitely a "work in progress".
On the bright side, no trees were harmed in the making of this drawing!
Regarding the box, it's 26H x 30D x49W. Target net volume 17 cu ft, 14.5 Hz tune. Port I.D. is around 8.375". It's a bit long at 35.25", but that does allow it to terminate nicely in the third brace.