Well Im a wood worker so my first thought is always wood. But im also paranoid at times. So I spent a lot of time researching this very subject before using a metal mail box.
If you would use a wood box once or even a few times it wood probably be ok. Trouble with a wood product is as it dries it changes. And wood will get to a point it has a flash feature. were very little heat or spark will send it up like gasoline.
I even thought of a lining to protect it but that don't stop the drying. the purpose for me to remove my smoke generator from my smoker was the fact there is a lot less chance for a fire. No grease and smoldering wood to come in contact with it. So adding any thing burnable to mine is out of the question. Especially since mine is indoors and I prefer the most safe set up I can have.
The following is just my opinion and not necessarily that of others on here. I add this because People have taken what I said wrong and it is recommended to do.
