I glued small very powerful magnet to underside and a similar sized disc to top of window. Sorts itself out when you open and close.
Nick, that sounds clever, got a photo ?
Sorry Jon I don't. I no longer have the roadster which was my everyday car, and because I've turned into the type of Morgan owner I used to mock (low mileage, never in bad weather) I haven't driven my plus4 with the hood up at all.
It was straightforward though. You need good glue for the rare earth magnet.For the disk on the perspex I just used a dab of super glue. It was an everflex hood. Magnet was probably half an inch in diameter. It was invisible under the flap. It would sometimes let go at really high speeds but fall back again as I slowed. Worked well.
Nick