Are wood trumpets susceptible to moisture like a wood box call? Would drawing cold, moist air thru the call change the sound? The delrin call makes sense in this situation. I know the majority of the sound is created in the mouthpiece but the body must play a role.
Yes it changes some and more of the change in sound comes from the mouthpiece like you said. Manmade materials like Delrin, PPSU, and Corian don't change much throughout the day like natural materials like ivory, buffalo horn, and bone do. They change a lot in just a few hours. Because there's not friction involved I wouldn't think the wood trumpet is effected as much as a box call, but more so by the changes in the mouthpiece. One longtime callmaker preaches this
Humidity where I hunt in central MS ranges from 10-100% and regularly spans 25-75% in a single day. Ive never noticed much difference from humidity in the Cox trumpet I use. How far the sound carries depending on atmospheric conditions is a different matter. The last two mornings had humidity in the 92+% range, but the humidity wasn't nearly as problematic as the 20mph gusting wind.
For these reasons why I pack and use hand Warmers .... I carry a backpack in my truck with all kinds of things I might need to fight off the elements / weather conditions during the turkey season ... Always have a first - Aid / extra snacks / bottles of water and toilet paper ...