My MGB Roadster from many years ago and the Triumph Spitfire somewhat more recently were both pretty much waterproof. My Mk1 MX-5 was excellent in that respect (just remember to keep the drain tubes clear... ).
Graham (G4FUJ)
Sold L44FOR 4/4 Giallo Fly '09 Gen2 MINI Cooper ragtop '90 LR 90 SW