First FG enclosure

I am getting ready for my first attempt at a FG enclosure. I've searched the posts and google and i cant find a way to calulate the interior volume of the enclosure. Any suggestions?

Also is there anything that you can think of that would make the job easier? i know its hard to do but i mean just like little tricks that you know that help a lot. 

Thanks

Ok well i started today. I think im just goign to make the box WAY too big and then calulate the interior size and just keep measuring till i get it right. Ill keep posting pix as i go along. Any advice along the way would be greatly appreciated!

As i said... IM making it a lot bigger than it needs to be! the Specs on the subs say to go with .5-1.5 cubic foot airspace or somethign like that. Ill check em again before i finish it. Im planning on doing both sides as well as the wall taht connects them. In there im goign to mold an amp(s) Im not tottaly sure what type im goign to get yet. Any suggestions? my audiobahns are the AWP312T. Audiobahn SAYS they are 1200RMS but audiobahn isnt always that honest apparently so who knows!

Oops damn link!!

Here's my example...my sub boxs' base is about 8 inches wide, and it sounds great!