Firstly, are you talking autosave and not backup?
And you probably have autosave on after preview
Here is the solution.
Enable autosave every 20 min this won't interfere with your new or demo capx files.
Next set keep up to 5 backups in folder when saving. (that is the only time it actually backs up, when you save... that is why I think you are talking about autosave)
Then create a folder, somewhere you don't go into at all. Call it C2 backups.
Now add that folder to location 1: Never to deactivate, I use Daily.
Now add a dropbox folder for location 2: weekly
Now add to copy folder for location 3: every 3 days.
So it will only autosave after 20 min. And you can disable daily backups or backup once per day.