Thanks for your post.
Yes I realise that flat surfice will suffer from torsional moment - twisting
(more than different shape 3 dimensional) and I will use sandwitch construction for better resistant.
And you are right - in my opinion 3 layers are ideal for the job.
However 3 layers of 100gr and 3 layers of 300-450 gr matt is going to result with different thickness of laminate.
That's why I ask members for help , to see how thick proffesional body is.
And there, where you can see the thickness of laminate is for shure that - that is stronger part with 1-2 layers more than on the rest of the body (archers over the tires, hood asamble, etc) or if the kit is from "brand" kit car factory - thats is how this has to be done.