I *think* garage walls are insulated. but not sure, never really needed to check.
I could close the enclosure for night, but it feels like that would suffocate the plants. Do plants have claustrophobia? Would they get less oxygen or the gaps will be enough?
Styrofoam board is cheaper .. So i will go with
this.
I will build enclosure tonight with some gap up top between the two light fixtures and will measure the temperature inside with the lights on at night.