I want to install wood grain finish panel on interior walls and on ceil
in my new construction.
The construction is a small inexpensive one room chalet (16' x 24')
I did it myself with some friends and I will spend there my weekends
and some vacation and is in Canada.
The wood grain finish panels are 4' x 8' sizes and thickness is 2.6
mm.
I would need some advice how to install them on the wall and on the
ceiling of the cathedral roof.
I want to avoid them to be undulated because of dilatation (expansion).
I did just add R-20 pink fiber glass insulation on the wall (studs is
2"x6" at 16" on center) and cover with 6 mil vapor barrier.
How should I put these panels in order to cover the walls and the ceil?

May I put them directly on studs in contact with vapor panel? Or is
better to use some horizontally furring strips?
Also I would not like to use a gypsum wallboard as a back support.

Thanks,
Chris