sub enclosure volume and port length?

Hello, I am very new to building enclosures, however I would rather do it myself than pay out the ass to have someone else do it for me. I am ordering an 18" Fi BTL N3 and the recommended ported box volume is between 4.5 and 10 cubic feet. My question is, how do I decide how big to actually make the box within those sizes? Is it more a space permits thing? Another thing I don't quite understand is the port length. I want to tune to around 32 hz, however I'm not real sure about the formula. I have browsed this site for awhile and read a lot of the subwoofer enclosure articles and also the DIY guide, but I still don't quite understand it. I know this is all going to end up a trial and error thing, and I'm prepared for that. I just want to know the correct way to do it so I don't spend more time than I need to tearing boxes out of my trunk. Any hints or tricks to better understanding this would be greatly appreciated. Thank you :)

decide what the maximum size you can make the box for your needs. (fits in the vehicle :)  )  Then contact the manufacturer of the woofer with your box volume, they will reccomend a port for your needs.  Without software or experience, you run the risk of a lot of problems otherwise!

If you do it right the first time you won't need any trial and error.  Start by reading the guides on this site and when you have specific questions, ask.Support the12volt.com