I've done sinew backed,hickory backed,and rawhide backed...and all will work fine if done right....but my favorite backing for juniperus virginiana is sinew backed,even tho its a lil more effort to do its worth it in the end
if you have good ash backers I'm sure that would work well too....what does he draw weight and length? What style of bows does he favor best? If he doesn't like short bows then maybe sinew isn't the best answer for him and a hardwood backing and longer bow is? Lots of options,styles,and choices,and it just depends on what cranks his shaft and personal preferences