I'm pretty sure the base of the Reed is made out of stainless steel. Aluminum would be much lighter. A stainless steel arm board would be real nice but would cost a pretty penny to fabricate. Steve Dobbins uses stainless steel arm boards on his latest incarnation of The Beat I believe. I made an armboard out of african blackwood which is one of the most dense hardwoods and it sounds quite good under my Reed. I may have a SS arm board made one of these days though.
Sean
Sean