I think Rob's suggestion is the most appropriate, so I'll just mention two things.

First, Google Docs is called Google Drive now, and it's not all-online. It can have that option, but it can also work entirely like Dropbox if you want it to.

Second, as others have mentioned, your Dropbox folder can be anywhere you want it to be located. Going even further, you don't even have to move the Dropbox folder. In the past I've used symbolic links in Windows to make Dropbox back up folders that weren't really located in the Dropbox folder. You could then create a folder in your root C: drive and make Dropbox think it's also located inside it's own folder. That should get around the character length limit...