Hey JT,
I live in Northern Michigan and our humidity is way high also....all year around, even the other day we had -5 and 62% go figure. I've made bows with both bamboo and hickory backing. They both worked very well.....usually I prefer the hickory. Also I use TBII for glue and have not had any trouble at all with losing performance or set issues etc. I also use spruce pitch and grease for the finish (NA Style) and dont really know if that makes a difference or not.....it's just what I use is all.
Hope that helps ya out a little.
rich