Just to let everyone know I have solved this issue now, and thought I
should share it with the group in case anyone else encounters the same
problem.
I swapped the editor type to 'Other' and renamed my FCKEditor install
directory so that it didn't include the word 'fckeditor' - if the word
'fckeditor' is present, RedDot assumes you want to use the default
version.
The following data was input into the two input boxes presented:
URL of external editor:
The path to the editor e.g. 'cms_editor/editor.asp'
Name of the element that contains the text that should be stored:
The variable which stores the rich text before writing it into the CMS
DB. In the case of FCKEditor it is "FCKEditor"