ok So i picked these up new for free from a buddy who's had them sitting in his garage. They are being run by my jl 500/1 that I have. The box they came with rattles and i want to build a new box that hopefully will make these sound a little better for two 12" these are the specs that i can find about them.

RMS: 700W
SPL: 90dB
FREQUENCY: 30Hz-1000Hz

These are the current dimensions for the box they are in
WxDxH: 34.5"x15.5"x15"

These are exactly what i have

I read the how to but i have no clue on how i can calculate a good box for these with the info i have. A little help is greatly appreciated. I dont want to just go buy a box from a pawn shop or something for two 12's id like to learn how to make box's for future subs.

Any ideas or suggestions on what i should do to make a good ported box for these?

Its going into a ford winstar minivan size honestly doesnt matter to much as its going into a van.