My DH made me a wood box planter using cedar it is around the same size as you want to use. I have used it to grow tomatoes for years, it is still in very good shape and not deteriorating as of this time. I leave the soil in it year round in spring when planting a portion of the old soil is removed and some new soil added. The tomato plants grow and produce well each year, he did add a built in support system for the plants using those plastic coated heavier garden stakes.
Added: our container is sitting on cement which likely contributes to it lasting a long time.
