Thank a lot guys for your kind comments.
Hisham, some tanks were painted sand and brown during trials in desert conditions but they not operational tanks. Later, when French deployed tanks in the Gulf for common exercises with UAE army for instance, the tanks were covered with some sand and brown camo nets over the 3-tone camo.
Joel, I don't use X-20 any longer since I've discovered that alcohol is good for the job. Concerning the ratio thinner/paint, for this camo I applied 80/20 approximately. As I don't use the pre-shading technique, I generally have a 70/30 ratio for the base color then I thinned a bit more the covering ones.
Karl, figures are not my favorite part of modeling but I must admit they give some life to a model.
Olivier