Here are the external dimensions for a box to hold a 12 inch speaker that will fit in the trunk; 10x25x13. If in doubt on a box size then just get some cardboard and make a box to check for fit. I have a kicker 12l7 in mine, sealed. Before displacement the internal cu. is 1.33. To be honest though, I should've went with a really good 10 in a very large ported box as opposed to a 12 in a somewhat small sealed. You're choice.

 

Zenclosures box

 

Damn..^^ that takes up the whole trunk space.....not good

 

+1 for this.

 

The ZEnclosures box is nice... maybe someone who has it can take measurements for you.
Buying it is not too expensive either.

 

+1 for the Zenclosures box. If you really insist on making it yourself(Zencl. quality is tip top), someone did post the dimensions for their box on here in this subforum once before....

 

It does take up a some room. It's not as tall as the picture makes it look. I still have storage on the sides and can easily reach over it to place things behind it. I don't have to worry about it moving around, nor do I have to do anything special to secure it. I rarely use my trunk for much. Plus, I can take it out without any problem. Not the best option if space is a concern, but certainly an option.