Dropbox works really well with KP and I used it for years. The problem was that I ended up with more devices than Dropbox supported for free so I switched to Syncthing. If you only have three devices use Dropbox.
Syncing with Dropbox worked well for me. When you deal with an adversarial server holding your ciphertexts, you have to be a bit careful with the encryption. But keepass is good, AFAIK.
Syncthing improves the security, for instance, just in case a vulnerability creeps into the keepass code.
It works, but I had problems with the Windows Dropbox client failing... silently, so my wife and I would end up with different versions of files, or not being able to "send" them to each other because her client was down and we wouldn't know.
Syncthing works, has no central server to be beholden to, is free, and I have much more stability with it.
