You don't need a password to protect the BC logical drive. I had security concerns about this as well and learned that all you have to do is terminate BoxCryptor and the logical drive will immediately disappear. The decrypted files in the drive are then no longer available. To get access again, just start BoxCryptor again and provide your encryption password.
The only additional advice I have is to make sure you uncheck the "Remember password" box when you start BoxCryptor, otherwise anyone who gets access to your computer/notebook/tablet will have unlimited access to your unencrypted data.