Is there a way to do this in PlayCanvas using the default PBR shader, or is a shader chunk needed?
Do you mean like this:
https://playcanvas.com/project/362235/overview/tutorial-cube-map-refraction
That works well in that scene, I have a skybox that looks sort of bad when applied to some glasses on a table, it’s good for the scene but not for interior glass models unfortunately.They’re so thin I can’t tell if it’s working either way 
I tried replicating that setup, think it’s My models
https://playcanvas.com/editor/scene/542453
I appreciate you setting that up so quickly BTW!
BTW again, is it me, or is the refraction change global if there is more than one material setup this way?
Mike
I got it working, I put a different cubemap in with a prefilter and it suddenly worked.
Answered all my own questions Just needed to put in the new cubemap and then put back the one I was using, caching I bet you.
https://playcanvas.com/editor/scene/542453
Thanks Will, this does what I needed to do.