Is it possible to use the SdCard in portable mode but encrypt it? I dislike how the internal sdcard formating works, I don't want to replace the internal storage with my sdcard, my target would be to extend the storage.

Mainly, I use the sdcard as storage for the camera and personal data. I really want to encrypt this data.

Is it possible to use internal (for example 8gb) and external storage (64gb) resulting in 72gb total storage. accessing it via usb cable on the PC but not only encrypt the internal storage but also the external?

edit:

Extra question/Clearification:
I want encryption of the internal and external sd (no matter how its called "portable mode" or "internal mode"), keeping the sytem data and the apps on the fast internal sd but also have my data encrypted on the slow external sd. also i don't want to loose storage space, so it should be an "and" not an "or". is there some tutorial how to archive that? root access is available
It is not possible using the Android encryption of Marshmallow. Disk Encryption encompasses internal and external SD in the case of adoptable-storage and only internal SD in the case of portable storage ( since the external SD is considered a part of SD in the former)

Full Disk Encryption mentions other possibilities of encryption and does not cover what you wish to achieve. 

You may need to use a third party app, like SSE universal encryption, or other apps to encrypt files on external SD. I haven't tried this app but mentioning being open source and hence perhaps better