I just put this together this year with 4 sheets of 2" foam insulation, 4’x8’ sheets (top, 2 sides and one cut in half for the ends). The one on the floor is just 1/2" thick, may not be necessary. This is in the 2nd story of an unheated garage. I’m still using fluorescents which works out well as they give off just the right amount of heat to keep the interior at 75-80 degrees. I have the lights on a timer, and a small electric heater with a thermostat keeps the inside warm at night when the lights go out. I stuck an instant read thermometer for cooking though the side so I can check the interior temp without opening the end. I may add a vent or 2 so I can control heat, I think the temps could get above 90 F as the garage heats up. The sheets are foil back, but I kept the white side in as it’s supposed to be more reflective. I’ll have to rebuild the PVC light holders to improve the layout inside, perhaps even set it up to hold another sheet of insulation or plywood to create 2 levels and add 4 more lights. I wanted to be able to break this down for storage. The wood was attached with construction adhesive, but it’s not sticking to the foil well, I may have to ad a couple slats inside and screw through to the outside slats to ad some structure. Otherwise its pretty stable. I cut the tape on the ends to get in and out right now. I’ll need to improve on that and I may add a plexi-glass window.