Is it more a function of a stubborn neck than of humidity? JH has suggested using the pre-setting technique used on older Ricks for newer ones that resist adjustment. That way the rods can simply hold the neck in place instead of having to move it into place.
I've always wanted a "4381" model bass. Did you make and set the nec? What are you gonna use for hardware? There was a 4005 tailpiece on Ebay last time I looked.