I have a few Prusa i3 MK2S' at school and want to install Octoprint on a Raspberry Pi 3.
The issue is that due to security concerns, the school will not port forward to the raspberry pi.
I have a VPS that runs softether, and was wondering if it was possible to tunnel the web interface through the VPN to display via the VPS's IP address.
I don't see why should not be possible, but it might require some port forward rules also.
Access using a cloud solution is not a good alternative for you? Look for a plugin called Octoprint Anywhere. It's very simple. Only allow webcam, pause/resume and cancel job, but these are the most important functions to do remotely.
Take a look at the video here:
Octoprint Anywhere
There is another one that is more complete, called Astroprint Cloud.
Here's how this works:
Astroprint Cloud
Video
Octoprint Anywhere probably wouldn't work out, as lots of users need access to the same printers.
Same with Astroprint
Having been an I.T. Manager, I'd suggest working with the school's I.T. people to create a solution. They won't like it if you're doing something without their knowledge.