I refurbed a triumph spitfire heater, as its small and compact and suits the look of a cobra interior. But I just pulled it out in favour of one of these:
Heaters : T7Design.co.uk, Lightweight Kit Car Heaters
its a small company, Adam the guy in charge will talk you through whatever you want to know. Same product is also available via boat stores (at inflated prices) or via his T7 ebay shop.
The T7 Modular heater just arrived today and it is excellent quality and good value for money, and doesnt take up much space. Havent actually tried its defrost and blower capabilities yet i should add, but loads of good reviews for this product on the web.