One nice trick from the yamadori video that I learned was to drill holes (and a lot of them) smaller than the particle size of your aeration layer. Loved that little tidbit.
I think wood works great for training. The only thing I’d be careful of, is using chemically treated wood. I have two trees currently in training in wooden boxes made with some cedar off-cuts from when I built a fence in my side yard about a year and a half ago. Seems like a great way to reuse material, especially since cedar is naturally rot resistant.