ah, the fabulous Morgan Mark Up price! I think they're the same as mini ones (trad ones certainly are), and cost about £10 from most suppliers. There is a nice stainless steel upgrade that can be had for about £14 - https://www.minispares.com/product/Classic/500929MS.aspx

Based on what others have said, I have got neoprene on the inside, I have glued a plastic washer/spacer on the underside by the fixing screw and also very slightly (we're talking a mm or two) squashed top and bottom into a very slight oval shape to it catches on the top fastening, and doesn't pop off when I screw in the bottom.

1972 4/4 4 seater, 1981 MGB GT
1984 Harley Davidson Electra Glide, 1990 Kawasaki ZX10