Thank you Jan. Let's experiment with the turn fins. 
The turn fins are made of 2 mm aluminum. I know it is not the best choice but it is easy to replace them later on if they are not strong enough. I have also bought an 1 mm stainless steel plate but it is too difficult to process.
I totally agree with the fixation strategy. I ve used a latch in the Penarib and I also bought these rosettes for the various cowls:

The turn fins are made of 2 mm aluminum. I know it is not the best choice but it is easy to replace them later on if they are not strong enough. I have also bought an 1 mm stainless steel plate but it is too difficult to process.
I totally agree with the fixation strategy. I ve used a latch in the Penarib and I also bought these rosettes for the various cowls: