Me and some friends are going to start up some plants. so here is what I have for a grow box plan. There is insulation because its going to be in a shed outside durring this upcoming Maine winter it will probobly be two layers the first being regualar fiber glass house insulation(r-value of 4 to 6) and the seccond being rigid foam insulatioon(r-value of 1 or 2) with moisture barrier over it. Its also going to be built so it can be expanded easily to aaccomadate more than 1 or two plants they'll be 4x4x4' boxes made out of 1/4-1/2'' plywood. Power source will be from a standard house hold socket with extesion cord wraped with insulating and duct-tape, the fan will be about 6x6'' with the vent being 4x4'' I have crappy paint skills ask if you have questions
No it shouldn't be that bad I talked to the my science teacher who is also the agraculture teacher and she said that she growns mushrooms (for eating) in the winter is a small greenhouse inside a 3x3x3 and the lowest its gotten was 45 degrees that was inside a greehouse in a plywood box with no insulation and they grey fine and mines going to be in a half as small shed wish two layers of luan board in side a plywood box with lots of insulation, my guess it that it will be fine. and there will also be a fairly large light that hopfully wont burn, not sure of size, so maybe 60* minuim inside. there already 6" asnd there in my friends closet, but they have to be ouw by the end of this month when his old P.O. drops by to check in. and his parents smoke so they know what it smells like. so i eed to bang out a box or two by wednesday. so he can get them over because they'l get to hard to transport.
insulation probably wont do anything unless theres a heat source. It keeps heat in, and cold out, but if there is nothing making heat inside, once you open it up a few times to water/check on it, its going to stay cold. unless your light is going to make much heat.