If the plan is to write the files to the app folder then WebStorage is entirely useless; why are you guys pushing it so much?
You basically want to do this:
Make a global var called Root
+Is in preview
-Set Root to <Path to write files to>
+Is NOT in preview
-Set Root to NodeWebkit.AppFolder
Then, if using a dictionary to store save data...
+On Function "SaveGame" (or whatever)
-Write file to Root & <File Name> with contents Dictionary.AsJSON
The Root global var is used because, in preview, AppFolder returns the node webkit folder in the C2 install directory. More info here.
(Note all this is from memory so you might want to check out the manual if there are any problems)