I've used it with great success in my bathroom. Completely eradicated the condensation problem on the painted walls and ceiling. I also added it to the paint used to change the colour of the tiles - again great success!!
Originally it came as a sachet of granules but now it seems to come in liquid form. You add thermilate to the paint according to the instructions.
As I was using 2 colours, a bit of maths was needed to calculate the quantity of Thermilate required per litre of paint.
Check out their website.
http://tinyurl.com/ap7ovzw
There is good info in the FAQ and also a downloadable brochure (needs Adobe reader).
I'd also leave a window open slightly to allow the warm air/condensation to escape, or as you've suggested, having ventilators installed or lining the walls with polystyrene sheeting then papering over it .
Hope this helps. All the best.