I ordered this sandbox on the Ebay. Even if the seller said, it already had some kind of a weather protection, it felt like any pine without any protection. So I bought a wipe on gel for outdoor furniture.
I used a weed control fabric under the sandbox, which is screwed together. I followed all the plan, so it took less than 2 hours the build it, but I waited the night for the gel to dry (it should have been 24 hours, but the next day was already sunday…). I filled with 150 kg sand and had a back pain on the next day.