Wow, actually... that did work. I was using 'set GOPATH' and not 'export GOPATH'. I have GOPATH defined in my /etc/bash.bashrc... is there anywhere else I should be putting it?
Note that if you choose ~/go (instead of ~/Dev/go) then you don't even need a GOPATH environment variable, it is regarded as the default gopath by most of the go ecosystem >=1.8.
This is intended to save these moderately interesting headaches to many developers, which I find great so I encourage to go with the default path.
Cheers
Val