Rob, I deleted this because it was not working correctly for the moment. I did this procedure with other Garmins and it worked well but with the XT there was a problem. I know there is a problem with BaseCamp in combination with the ZumoXT. When you connect your zumo to BaseCamp only one of the two ToPoMaps Parts are shown. Garmin will fix this with one of the next updates.
I will send you an E- Mail tomorrow with the instructions anyway.