Correct. USE A VPN is the correct answer.
The internet is too dangerous to send LAN traffic over without encrypting the bejesus out of. I dont care how inconvenient that is. Failure to do so is how you end up with ransomware encrypting all your files, like with WannaCry.
SMB, Apple File Protocol, and NFS are NOT designed for insecure links. To use them, you need to establish a secured link over the untrusted network. That means an encrypted tunnel; EG-- a VPN.
Bear in mind that even if you set this up properly, you will likely run into asymmetrical bandwidth restrictions from your ISP(s). By this, I mean that most ISPs will throttle upload speeds to some fraction of a megabit, while giving you several megabits of bandwidth for download. To send data out to you at a remote location, your mycloud has to upload. If its upload speed is capped by your ISP, you are gonna get very slow access speeds. Same for uploading TO the mycloud as then the computer doing the upload to the mycloud will be what is throttled.
This kind of thing is really only useful when you have something like fiber to the home style internet, and have a good upload rate. Otherwise, it is likely to just cause you grief, and you should stick with things like FTP, or the MyCloud app types of access.