I havent been able to find box size recommendations for a pair of shivas or 12w3v2's. I think I want a sealed/ported combination for versatility sake. ...going for SQ with as much bump as I can get without being rediculous. Got plenty of room in the trunk. I listen to everything but especially rock, techno and rap.
I'll be running them on a JBL amp, either a 600.1 or 1200.1
For the the best results you should build your own box. To Adire specs that will give you the best sound instead of buying a premade box. And here is where you can find the specs on how big your box needs to be.