No it wont melt the plastic if you have any kind of exhaust at all. But you will have trouble keep the temp <80 with the door closed unless you have a very good setup for extracting the heat from the lamp. IMO a cooltube or somesuch is definitely called for here

Great setup!
altagid Reviewed by altagid on . Intresting Grow Room Set Up With GOOD PICS! My Grow Room Setup. Like to know what people think. also included in room: Digital Thermo-Hygrometer, Combo Nutrient and Grow Room Thermometer, ADWA EC Meter, soil dampness meter, PH Meter. the room isnt big but should be able to grow 3 plants. walls to be coverd in mylar and white/black reflective sheeting. Anyway love to know what people think or if we could make it better. Rating: 5