Completely cover the tank with plastic, down to the floor and seal it the best that you can. Bring an airline in from outside, maybe on a small air pump. Have it just loose under the plastic. What you want to do is create a positive pressure under the plastic, which will keep any fumes from coming into the "tent". This will also bring fresh air in for gas exchange. Don't run the lights, it would get pretty hot fully enclosed. Make sure that you are running fresh carbon just in case.