Making a dulcimer humidity resistant?
Instruments- discuss specific features, luthiers, instrument problems & questions
YOU ARE SERIOUSLY OVER-THINKING THIS WHOLE THING!
"-coating the inside of the dulcimer in something water protectant: an idea I had earlier that seemed to not be useful in general, but maybe in this context would help it hold up."
No, NO, NO! I live much closer to the ocean than your sister, and coating the inside will NOT work. If it did I would be doing it. For two years I lived less than 100 yards from the ocean on an island in the Pacific near the equator, one of the saltiest environments on the planet! If coating the inside would have worked I would have done it. IT DOES NOTHING!
-gluing in frets with a strong glue: in general I know that stronger glues tend to make maintenance and repair much more difficult, but if I want to build it to last, maybe I should glue them in with something heavy duty to reduce the chances of them shifting?
It is worth noting that I have traveled down there with dulcimers I have built and always had to pummel some raised frets every time I got there, so this is a primary concern for me.
You should not need to glue frets in if your slots are the proper width (not too wide), cut to the proper depth (not too shallow), and you have hammered/pressed them in properly. However, if you feel you must glue, use one of the slow setting Super Glues, as my friend John Knopf recommends will do the job.
Gel Packs -- WILL NOT WORK. Not the way you think. You'd need ten pounds of silica gel and it will only last a few days.
The fact is that the Dulcimer needs to adjust to the environment where it will live. If it can't because you sealed it up inside and out, one scratch will cause it to warp horribly. If the dulcimer can't adapt to local conditions because you artificially adjust it's local humidity with gel packs, it will warp the instant you let the humidity change.