@ mods not sure if this is the most appropriate section. We don't have a dedicated Airtightness one.          Time: 1hr.    Cost €60    Materials:    1 X Sheet of OSB or PlY  1 x Used car radiator fan including housing ( I used a lexus IS200)  1 X Roll of Airtightness tape.   1 X length of automotive wire.   2 x Crocodile clips.   2 x wire connectors.  Some short wood screws   Tools.