In your climate I would suggest not sinewing a hickory bow or a bow of that length. Like sinew and hide glue, hickory is very hygroscopic; meaning it readily takes on and releases moisture from the atmosphere). I built a replica of Jay Massey's Medicine Bow, sinew backed hickory with a rawhide covering., 60" long and when built, pulling 56#@26". After a month, it pulled 45#@26". Later on I sent it to a friend in Colorado to play with and before long it was over 60#@26". All due to the difference in R/H. This bow was sealed with one coat of Massey finish, 4 coats of Tru-Oil and a spray of satin poly.
The best way to prevent too much set is to be sure the wood is very dry, take your time tillering and don't overstress the bow while building it. Keep it in a hot box between building sessions. When done you can add reflex and toast the belly a bit to help out too.