Out of curiosity, I looked up the larch family in my tree book. Apparently there are 4 larch species in North America and my book refers to all of them interchangeably as tamaracks also. Western Tamarack/Larch and Eastern Tamarack/larch would be the likely woods available, with, as you said, the western being superior. However both weigh a hefty 39 lbs/cubic foot compared with 19 lbs for northern white cedar. They are all good in rot resistance tho. - Scott