if you are wedded to a Celestion V30 a closed back (sealed) cab is a bit harder to dial in than a speaker with known Thiele/Small (TS) parameters. Dr Z has done it:
Z- Best 2*12 cab black
and you could copy its ported design. The bottom end will be amazing.
also see: Interesting info on Thiele Cabs - Page 2 - The Gear Page
Many good designs are at Eminence, but for Pro series drivers, not guitar speakers:
Eminence - The Art and Science of Sound
I'd favor a 2.75 ft^3 ported 2 x Deltalite 2510 for solid to 60Hz bass which will destroy small buildings, at about the same size as the Dr Z. for ~$200