Artificially slow seasoning, strapping etc. help avoid drying distortion, but the true test with wych elm is to start tillering it. Only then will the stave reveal what it wants to do. As in, bend sideways so severely that the string lies three inches off the handle - and laboriously heat-correcting the bend will only make it come back upon the first couple redraws. Or the top limb, shaved down to exact same dimensions as the lower limb, suddenly pulls 40# while the lower one still pulls 60# (ie. all the bend is shifted to the upper limb). Not much you can do there, if a 60-pounder is what you want. YMMV.
Tuukka