buy two of these
www.homedepot.com/.../100396975
hook one up to your wall after cutting the hole (or a plywood window panel)
cut the angled part off of the other one, drill four holes, add sealant or weatherstrip to the mating edges,,,,,bolt up
then connect your hose to each end
if the outlet on your fan requires it,,,,,,use the cut off sheet metal to adapt the flat outlet to the fan exhaust face