Run the installer and pay attention to the options (usually radio buttons or folder selection screens).

Use the minimal install so BB uses very little of your C: drive.

Then put the RTs and RDs on the D: drive (likely faster than the external drive anyway). And point BB and RB to those D: drive folders during your install.

Ideally you end up installing the executable/license etc on C: along with the PGMusic fonts and such, but should be a small hit to the C: drive.

If you install RB I would take the time/effort to point its RTs and RDs to the same folders on D: and also create a new folder on D: called TempAudio, then in RB Preferences point the TempAudio directory to that new D: drive folder.
This saves drive wear on the OS drive (as well as load) because RB defaults to using a temp storage area on the C: drive for stashing the chunks of data needed for recording, audio edits, undo, etc otherwise.

Better to have that happening on a secondary drive so the program and OS have better access to the C: drive with less interruptions.

I do not work here, but the benefits are still awesome
Make your sound your own!