I wouldn't put any difference in between 속 and 안. We Korean usually use them interchangeable and mixed up like "속안", such as "이 속안에는 뭐가 들어있어?"(=What's in it?) But 겉 and 밖 are quite different. 밖 is just meaning "Outside", while 겉 has to be the "Exterior surface".

They are antonyms. 속 mean 'inside' 겉 mean 'outside' 안 mean 'in' 밖 mean 'out of'