Ok...here is the confession. I found it where I left it - in the aeroplane! Just as 440032 suggested yesterday.
I decided to search everywhere again. Searched two cars, the home shed, my office, the caravan, the hangar and the aeroplane again, yesterday afternoon. The plane had been searched three times by me and once by my wife, and it is only a small plane. I had even released seat catches and flipped up the seat bases.
So this morning I decided to go for a fly. Sitting in the pilot's seat, leaned the passenger seat back forward to tidy up the seat belts, and there it was in the seat back pocket. Black item against a black seat with a black mesh pocket. I must have actually leaned on it a couple of times it when I flipped the seat forward to search the luggage compartment.
It is more than just domestic blindness, because my wife usually finds things when I get desperate. Anyway, thanks everyone for your suggestions.