After more trials, finally I decided that this was the right position. The prefabricated alu strip was pre drilled with a small guide whole for drilling the fibre glass. After the predrill the alu holes and also the outer skin were drilled to the outer screw size. When the screws were inserted it pulled the inner skin to the alu strip between the outer skin. This ensured a solid and even finish. To use an alu profile guide was the suggestion from Dennis B. which were very helpful and made this task easy.
