First you follow the instructions for
Connecting to Tor before a VPN (User -> Tor -> VPN -> Internet)
Test if that works as expected.
Then you follow the instructions for
Connecting to Tor before a proxy (User -> Tor -> proxy -> Internet)
The following methods should work.
Proxy Settings Method
Proxyfier Method
The bullets points are all chapters on that page.
I don’t see why it shouldn’t be possible to use
User -> Tor -> VPN -> proxy -> Internet
that way. Once properly set up (follow the documentation and test), everything leaving the workstation is forced through the VPN by the workstation. And everything leaving the workstation is forced through Tor by the gateway. So now, when lets say the browser is configured to use a proxy, then it will hopefully [see documentation] do so. I.e. browser wants to connect to the proxy, and then the workstation forces it through the VPN, and then the gateway forces it through Tor. I am quite certain this would result in:
User -> Tor -> VPN -> proxy -> Internet