Grow box - cold temps

Box is in uninsulated outbuilding with no heat.... no other options due to security issue and too impatient to wait for another summer... cold temps are making this a real nightmare.... october to december-ish grow... temps during that time range from 0 degrees F to 50 degrees F.

CFL'S for lighting.... computer fan on top for exhaust with passive intake on bottom... small computer fan inside the box to provide air movement inside... box is insulated with sterofoam but still too cold.

I want to keep everything in box... so no external ceramic heaters or similar ideas.

Is it possible to use a line voltage thermostat mounted inside the box to control one or probably two incandescent light bulbs??? So when the temp gets below say 70-75... the light bulbs turn on until proper temp is reached and then back off.

Kinda a goofy idea but I really don't want a heater inside the box.

Maybe use an HID bulb instead of the CFL's?

i don't have the height available.... 2X2X3..... going for short auto flowering plants.... so i can use 24/0 light schedule.... to keep the temp up there.

plus i already bought the cfl's... limited cash flow as usual!

anyone else have any thoughts???

im having the same issues so im looking at 12v car heaters, this will only help smaller growing spaces ofcourse (at least im hoping) but other than using a space heater, thats the best thing i can come up with. hope that helps