Dropbox is great - My files are always safe in the clouds, and I can access all of my writing from my phone
"having a solely cloud based copy is not convenient for me" Not sure about all the cloud storage services, but with Dropbox you DO have a copy on each computer or device that is set up for your account. You can edit any one of those copies. The service then copies any updates to the cloud and all those other computers.
Hm.... I have learned something today! I was always under the assumption that the Dropbox folder was not accessible without internet. Seriously, never even tried to access the files therein when internet was down. I just gave it a go and you are correct!
I have all of my important files (writing, pics, music, etc.) on my internal HD plus 2 external HDs. Files that I use regularly (writing, work stuff, etc.) I have in dropbox as well so I can access them at anytime without having to worry about forgetting a flash drive or something. I have wi-fi everywhere I work so I always have access to dropbox. If you do all the free stuff they offer you can get a couple GBs of space for free.