...I have a friend who is an exceptional machinist. He also has a strong interest in cars etc.... he would love to design and make a sliding canopy, aircraft style that could be retro fitted to M3Ws. ...
Not sure about the "sliding" part. But certainly a screen + weather protection device, like a trad hardtop (per the +6 for example).
Challenges would be
- accomodating a luggage rack
- disassembly and in-car storage if touring
- ventilation / condensation / wipers
- vibration proofing
I'd suggest a roof canopy, maybe canvas, attaching to a varient of the Fairbourne. Suggest your mate has a chat to them as they had some thoughts re a roof for a 5sp... or maybe the factory would be interested in a chat?