How would one go about being a rationalist "with the serial numbers filed off".

There is plenty of support for rationality science and math in Arab history. There is probably plenty of support for rationality in the koran. While in Morocco, there is no reason to flaunt your atheism or disdain for much of what religion concludes: this is the shiny tip of the iceberg to a rationality you are developing whose real benefits are from the much more massive rational workings under the surface. So you could learn the support for rationality in the koran and the islamic traditions, and in any discussions cite these as support for a more rational position.

Just an idea that occurred to me.