One trick to use when jury rigging a darkroom is the application of rubylith masking film to windows and other light sources that you cannot permanently block. Rubylith film is basically just a large filter that blocks the wavelengths to which your photo paper is sensitive. For instance, I have a small window in the basement where my darkroom is. It would be easy enough to board over it...but it is not my house, so I cannot. Also, it is nice sometimes to not completely block out a light source, but to simply filter it and use it as a safelight. What I did is to coat a pane of Plexiglass with it to make a giant filter, and I wedge this against the window. You can also apply the rubylith directly to a window, if it is your house. I also stuff cracks with aluminum foil. It is cheap, easily formable, and does not require any adhesive.