You cant FTP into a Skybox F5 they are a closed source receiver and not Linux Enigma2 so have no /usr/keys folder either, you can though create a CCcam.cfg file with just the line details inside it place onto a USB stick and upload via the box itself.
Or goto the Network setting in the main menu if you cant see the camd option try entering 6666 into the remote while in the network setting to unhide the menu once inside there you can enter the line details manually via the remote, the USB method is a lot quicker