Use a piece of linoleum as a the curtain....velcrow the outside frame of the window with self-adhesive male-velcrow. Fix the fussy side of the velcrow onto the specially cut linoleum with staples. Mount this onto the window when you need to use the darkroom....take it off after you finish using the darkroom. For additional safety pull your regular curtain over it. The gaps in the door can be temporary sealed with an old towel. My cost of light proofing the room is about Sgd10.00. BTW, I have mounted the Nova processor on a roller tray...same as those that are used to mount the washing machine or fridge. Push it out for better work flow and back to save space.
FYI, my room is air-cond.....so very comfortable to work in.
Happy printing!!!