I may have changed my mind on this and will use the green house parts to make a lean to greenhouse to go against my allotment shed. As this has a brick wall this should be a good heat sink. The qusetion still remain however about using screws and bolts.
To expand a little, I was a Science teacher for many years and know that Aluminium will react with metals lower in the Reactivity Series. This can mean that it you use screws made of steel they will react with the aluminium once they get wet. In practice, this seems to mean that screws will rust up very quickly. Can anyone advise on this?