I have the same setup, for the most part, My cab is 24"x 24"x 50". I have a vanity light bar from my local home improvement store (3 Bulb) That I hung from the top, and I also have a 4 Bulb, 4ft, tube floro that I attached to the back wall. I will start a thread for you guys to check out.

But anyway, Keep the intake hole and use the fan from it to add to the exhaust. Make another hole at the top about 3-6 inches to the opposite side and mount it as exhaust. To keep dirt and light from getting in thru the intake, I use a dryer sheet to keep dust and dirt out and a piece of foil or dark plastic on the inside that would act as a flap that opens while the exhaust is on and will fall as the exhaust turns off, usually when the light goes out or shortly after, on a separate timer.

the cfls wont cause too much heat, so the 2 PC fans should be adequate. You may need another intake vent, but that's easy. Also, if the temps don't drop, try getting rid of the Mylar/foil shiny stuff and paint the walls a satin white. White is extremely reflective and also deflects heat. metals or shiny mirror like surfaces retain heat. Think of foil and how it helps retain heat and cook your food. Its essentially doing the same to your plant.

Lemme know,