Sialis.org will tell you about gourds etc for bluebirds.
My gourds mostly get house wrens. One guy works so hard and almost fills even the biggest gourd with twigs!
A good mature gourd can have a shell over an eighth inch thick. I want to say 1/4 inch but I might be overstating.
Gourds that I leave whole and rolling around the garden for fun can last YEARS.. and one that was cut, painted, and hung and used by birds is still in one piece at least 10 years later.
I have one big one with a nice handle, all dried and rattley.
Yes I can imagine it taking a long time to dry, there, Kat. And they smell funky
