Mark,
Might be worth following up OAMPS Aviation - they used to insure trikes - had my first trike insured with them (theft/fire/driving) about 7 or 8 years ago ... paid the premium for a couple of years, then decided it was a bit of a waste of money - so stopped ... of course ... about 18 months later trike gets knocked off out of the driveway, never to be seen again.
The OAMPS website still specifically mentions sports and experimental aircraft, ultralights and hang gliders .. but doesnt say anything about trikes
David