Jason,
Thanks for the reply. I got the aquapanel and heating mat laid today, so I'm going to try the multibase tomorrow morning.
I had a bit of an anxious moment when I checked the resistance of the mat after I'd laid it and it showed open circuit. Turns out I'd just got the multimeter on too low a setting.
I didn't actually realise that multibase was a self-levelling compound! Good job I posted the question. Will I need to smooth it out with a float at all, or is it so runny that you just pour it on and leave it to settle on it's own?
When you mention latexing, are you referring to the multibase, or is there someting else I should be laying on top of the multibase before the flexible tile adhesive?
Also, how long should I leave it before beginning the tiling?
Thanks for the brilliant pointers so far.