What's the best way to integrate Dropbox directly to my OP box?
What are you attempting to do with your Dropbox?
Upload files directly from it.
I know there's a plugin for uploading timelapses to DropBox, however what you might want to do is look into using git to do what you're thinking of. Basically, upload gcode to git, and have a watcher pull the files to the OctoPrint setup. There are many tutorials on how to do this on the internet. I'd also look at the timelapse to Dropbox plugin for a better idea on how to make your own plugin to possibly suit your needs.