Tiling onto Dry-lying in the bathroom

I have dry lined all Exterior walls from the inside with Quinntherm 38mm drylying in my new build. My plumber has asked me to check out tiling onto Dry-lying in the bathrooms as he has concerns it is not as reliable as tiling onto a block wall and there maybe water leak issues.

Has anyone done this and are there any watchouts ?
ie using a flexible grout ?
Should I spray the dry lying with a waterproof spray to avoid water getting through the dry lying ?

Have you used moisture resistant plasterboard in your bathroom.If you used standard plasterboard you really should plaster it and then tile on top of this.I was told in the past that you should not tile onto a smooth plastered surface but I have always used the correct grout (the grout u mix on site rather than the pre-mixed stuff) and have never had a problem.
Do you intend dry-lining the ceilings, it may well be worth it.If you are not plastering the plasterboard you really will need moisture resistant plasterboard that will be fully taped and jointed to keep the ceiling where it should be.
I am a Kingspan fan, did you find a big difference in price between kingspan and Quinntherm.

Regards,
Wex dude