Car will have no windscreen and so no need for demisters ...
However it will have a gaping cockpit hole that needs heating , probably most of the time it is being driven ?
thanks for the offer of the mini one , I am still drawn to a ' new ' one from Ebay fingers crossed they don't leak hence asking on here if anyone has used them ?
I've an old MGB that I drive most of the year with roof off (still got windscreen), but doesn't have a heater. I guess it's what you get used to. A mate had a Caterham that I remember we went from Bath to the factory in Dartford in January with roof off. Warm as toast in flying jackets!
Mygassers link looks interesting for demisting when roof is up.