I was able to get an extra 20GB in my Dropbox by following the steps below -
1) sign up to Thingiverse
2) once you've signed up and logged in, click on "Explore" and then "Things".
3) randomly choose a thing
4) Click the “Download all Files” button on any Thing page on Thingiverse.
5) Click the “Claim Now” in the modal to claim the offer.
6) Thingiverse will redirect you to the Dropbox authentication page on a separate tab or pop-up.
7) Sign in or create a Dropbox account.
8) Authorize Thingiverse to access your Dropbox account information (It won’t have access to your files or folders)
9) delete your Thingiverse account. The 20GB storage will still remain.