Went through all my sites and added 301 redirects so that only one version of the site exists. It had been in the back of my mind for some time so I am glad it is out of the way. While I was doing this work, I thought I'd go back and purchase the plural of the name of one of my sites to avoid confusion for my site users. Unfortunately, someone bought the domain name two days ago. Bummer.
Anyway, I uses the instructions for the 301 redirect here: