Stepfix,
Here's how I do it:
I create a new, blank, empty catalog in Lightroom. This will be my working catalog.
I import a new shoot into that empty catalog with the RAW files going from my memory card onto my c: drive and also copy the raw files to my master external g: drive.
I actually use Windows Explorer to make the copy once the import is complete but could
easily set Lightroom to backup the RAW files to the external g: drive while it does the import.
I then process the shoot referencing the RAW files on my c: drive.
Any RAW files that I don't want I mark as Rejects, but I don't delete them yet.
When the processing is done, I close Lightroom.
Using Windows Explorer I move or delete the RAW files from my c: drive.
I re-open the working catalog.
Lightroom can't find the RAW files so the folder(s) goes red.
I right click on the red folder and select "Locate Missing Folder".
I point Lightroom to the folder on my external g: drive.
The folder goes back to white when Lightroom has found all the RAW files on the g: drive.
I now delete all the photos in my working catalog that I have marked as Rejects.
I optimise my working catalog & relaunch Lightroom, using the option in Catalog Settings.
I open my large, master catalog.
I then "Import from Catalog" my small newly processed working catalog.
I then optimise the master catalog,
I close Lightroom and make a copy of the master catalog's lrcat file, just to be safe.
For clarity, I use the following folder structure:
I save my RAW files in C:/Data/Digital Photos/Folder Name on my internal hard drive
and on G:/Data/Digital Photos/Folder Name on my external hard drive.
This way it's quick and simple for Lightroom to find the missing RAW files when I do "Locate Missing Folder" in the Library module.
I have a similar folder structure on my laptop, so if I expect to work on my working catalog while away, I simply copy the RAW files and the working catalog lrcat file to my laptop. When I return to my Desktop PC at home, I just copy the lrcat file back to my Desktop PC and carry on. Lightroom doesn't know that I've swapped from Laptop to Desktop.
Hope some of this helps,
John