A quick update - the customer now has electric sockets in the middle of the room and no sign of a swimming pool.
things got delayed a week as hire company supposed to be supplying the Flir camera got confused and got in a non contact thermometer instead!
I ended up up buying a Flir One for iOS as well as hiring the i7 and have to say the Flir One is a great bit of kit for 200 quid and was invaluable in setting everything out before I started, highly recommended.
thanks for all of the helpful comments and suggestions
paul