Thanks, that did help a lot! The HTML/CSS side is working now somewhat but I still have 3 odd bugs when I switch between scenes.
My test project - https://playcanvas.com/editor/scene/480406/launch
1) I get a null error very randomly after switching scenes back and forth 10-30 times
on this function call - "pc.app.root.findByName('ModelViewer').destroy();"
2) Look at the ram on Chrome go up to 1gb if you switch scenes 30 or so times (I can reproduce this bug every time).
3) I loose the event listener on my back button after 10 - 30 scene switches.... or the z-index gets broken or something else ... not sure yet.
There is still a few things that I can try and I have only spent 6 or so hours debugging it so will carry on with different methods tomorrow. I might try to not use the scene feature in PC and instead just hide and show the models when I need them. If you have any tips on hiding and showing the models it would be appreciated as I cannot find it in the api reference.
Loving playcanvas so far, despite its quirks! And very happy to see good + quick responses in the forum, it makes all the difference thank you so much.