Are there updated instructions for installing Gapps on Sail X?

I tried this, but:

• /opt/alien/system/priv-app no longer exists (there is an extra layer now, /opt/alien/rootfs/system/priv-app)
• I get "Read-only file system" errors

This is on XA2, SFOS is 4.5.0.21.

EDIT:
Never mind, it looks like a known problem. The solution, if one exists, is almost certainly beyond my capabilities. I should have done my homework before forking out 40£ and 50€. Oh well.