There's no standard way to do this. The Dropbox option is a great idea. You have to manually sync them. I recently had to sync my home system with my system on my desk at my TV station. I copied the whole Motion Templates folder to a drive from work. Took it home, and one by one, in the work copy, go to each folder (Titles, Generators, Effects, etc) and copy. Then go to the folder on my home iMacPro and Paste. I'd get a warning about replacing existing files, to which I told OSX to skip all file copies. Then I made a copy of my home folder, took it to the office and repeated the process. They're both in sync now.
Going forward, I have a Project in Frame.IO now that is for this purpose. Basically doing what you're going to do in DropBox. Whenever I get a new template, I'll add it to that for a completed Master Copy.
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