The grow light people who study these things say that flat white paint is a better reflector than foil, so if you just paint the inside of the box you'll be better off.
I'm afraid, though, that even with the best reflectors inside, those two lights will not be adequate.
I wouldn't worry too much about the temperature—the box will help hold in any heat from the lights. Besides, warm temperatures combined with low light will guarantee lanky, soft growth.
