Patrick Bouclans, a friend of mine who is THE specialist of the Mirage 5 gived me some informations about the closed doors:
Engine shut down and accus empty, the doors are open.
When the engine is on, the doors are closing themselves.
...But you can also close them manually...
...Anyway, I want the doors open on my aircraft!

So I have begun the work. Slowly, to avoid to damage the part. One door ready; must continue with the second one and then to make nice wheel bays...