subwoofer box dimensions needed

I would.  I would use a baffle on each side, halfway back from the face.  Large hole cut in the center, like this:

They have to fit snug, so at this stage of the construction getting them into place could be troublesome.

If you don't have the material to cut a full baffle for each side, you could do it another way.  Again, on each side halfway back but using scrap pieces of material, something like this:

You would have a rock solid enclosure that will give you all the SPL these subs will put out.  The box won't be stealing any of it away with flexing.

Nice job so far.  She's looking more attractive all the time.