Yeah, so far root has been a bigger issue than ma5 for installing on WSL. More info soon, but for reference, 'source thisroot.sh' was the correct command for me.
If you happen to know the person responsible for naming a package that likes to live in *nix 'root', please do pinch them for me.
I am also sourcing the file here (it is actually embedded within my bashrc ;) )
I don't know him personally. He works at CERN :)