I too would clearly prefer polypropylene or polyethylene over wood. Wood can split, wooden box are often glued and the glue will be chemically weak, and so on.
If the list says that EPDM is good at sodium hydroxide, don't worry more. Such lists are meant for 24/7 flow at chemical industries, a small occasional leak is easier. Strong mineral alkalis (NaOH, KOH...) act essentially all the same.
Bleach is not sodium hydroxide - provided the commercial description uses the words properly. Elsewhere in Europe, sodium hydroxide is easy to find as a washbasin unlocker; at the store, the package carries a "corrosive" warning picture and contains a powder, then you can check the composition for sodium hydroxide.
I have no doubts about Epdm, but trying on the wooden box may be interesting.