A lot of cars I've seen do have them bolted down through the leather and rubber padding. I don't know how much the base might move with wind pressure. Once you start drilling you are past the point of no return The screens come with screws....they do need to be replaced with bolts...and large washers.
It may be another year before Steve Simmonds gets round to having a new batch of mounts made .... Be warned, they cost more than the screens, a lot more! He told me that the bolt holes are the same as the standard feet so the scuttle will not need re drilling.
Jays Former Morgan owner. Gone but hopefully not forgotten!
The screens come with screws....they do need to be replaced with bolts...and large washers.