Thanks for all responses. I just requested joining information from AOPA Belgium by e-mail - will see what comes next.
@Genghis: we do have a Belgian ULM federation, and I do am be a member and even occasional collaborator, but they have repeatedly disappointed me with their enthusiastic lack of earnest. Even if we are amateur fliers, our publications - on paper and on the www - should have a certain level of professionalism. Your suggestion of joining the BMAA merits consideration, at the least.