Citroen Specials Club - the club for all lightweight cyclecars

Whats the best cover for the spare wheel on a Lomax or is there an easy way to make a cover ( dustbin lid modified etc )? Im trying to keep the fierce Algarve sun off the top mounted wheel . All ideas welcome .

any material like a tonneau cover should be ok, and have it sewn up and a pull cord to tighten or elastic...