Haven’t found this anywhere else so here it is.
To backup a project to Dropbox, simply duplicate it and name it "Dropbox.spritepack/‘your project name’ "
Then go into a project and sync your Dropbox folder,and you are done! You now have a backup copy in the cloud.
Sadly there is no way to retrieve it from codea, but atleast you have a copy somewhere.
Hope this helps someone else, it’s a life saver for me.
I only hope that one day there is a plist entry for project locations 
Dave
I find it pretty amusing that this works 
tricky - I have just been copying the project and mailing it to myself. It would be great to have a Codea option where this happened automagically (and even better if you could retrieve it).
Just a quick update since the last update 1.4.3.
Using the “Dropbox.spritepack/” update method now saves a version in the dropbox folder AND the main user docs. NOTE at this point your only sending a copy to dropbox, the version in your docs folder doesn’t get backed up after duplication.
does this hack still work?