Doesn’t have to be made of wood. You can use anything that will give shelter. I like the drain tile it does give a bit of insulation. Here is a link to the tubes I bought.
https://www.amazon.com/dp/B0CSZ9WM68?psc=1&ref=ppx_yo2ov_dt_b_product_details
Hang under a roof edge where it will not get rained on. Bring into your barn with the first freeze and keep it in there for the winter. You can take it out in March. Important factoid, make a bag of organza. It will keep mites from bothering the larva. And in the spring if you are late hanging them up, any bees in the bag are just moving slow because of the cold. They will be fine. We never bought any larva or made a special mud pit.
Great advice! Thanks! :)