sweet!! the 15 is from bottom to top of opening.. i believe those were the correct measurements...?
Here's what I would do.
You'll wanna compeat for every inch of hight you can get, so custom make your pots. Drill dranage holes and cut to specific hight. I'll give my recomended mesurments at the end.
Plan on using lst and topping to keep em short and wide.
Mylar the thing up nice and neat. Those silver looking reflective sun sheilds for car windows work nice, or emergency blankets from a dollar store. If none of that give a few good coats of FLAT WHITE PAINT.
Going for 4, 42 watt CFL lights.
They are Approx, 2 3/4" wide. 6.5" long.
You can use aluminum foil tape with CFL's for the top reflective part. You'll need to mount sockets to the top after, so the bulbs are lenghtwise against the top, but the bulb shouldn't touch. Just a few millimeters is enough.
I would mount in a "X pattern on the top. Sockets to the outside, bulb towards the center. Keep even spacing in mind and how you will position the plants under them .
Because of the shortness, i would say 2 computer fans for EXHAUST. And for air intake i would drill many 1/4" holes in the floor of the cab. (assumin there's a space under there to draw air from.) If not we'll have to work out something else.
You have 15 inches of hight to work with.
-3 inches at top for CFL"s
Make some pot's outta something you find like protien shake container. Cut it down to like 4" make sure it's wider for more roots, shoot for 6-8 inches.
This leaves you with 8" of space for the plant to grow. You'll have to top it after 3rd or 4th node, you'll need to do 12/12 light cycle from seed. And tie down branches to the pots, but it can all be done very easily, and I'm doing it with my own.