There have been posts that users have installed to a usb drive but no one have reported how long it works. What kind of computer do you have. If it's a desktop you should be able to add a second drive very easily. If it's a laptop you can get a larger drive and image the old one to the new one then swap them. Some laptops even have the ability to add an extra drive. The data rate on a usb drive will be slower then a drive connected to the motherboard. The only big problem I see if you have a laptop is any external connection could be reset should you disconnect the devices and use the laptop at a different location. Although I have though about Windows 10 with Microsoft OneDrive. I personally have reservations about my data being in the public domain (cloud storage). Data centers do go off line. Although data centers are are more reliable then your local cable company. There's always a nas box. Might get a better data rate because of the network connection. With things getting smaller, faster, and less complicated - I can't see making it larger, slower, and more complicated. Amazon has a Hitachi 2TB 7200rpm drive $43.99. Amazon Prime and in 2 days and a couple hours work. When I was in data processing class we were taught KISS (keep it simple stupid).
The best I can describe this is your hanging over a very deep canyon and your holding on to kite string.
Good luck.
