I saw a very respectable brewery rinse their barrels with idophor, but I personally have zero experience. Please regard this post as a shot in the dark, and something I would do because I'm stupid. But if it were me, I would soak it in RO water for a while to saturate the wood, then Idophor for a while after that to sanitize. It might have termites or something, but after it soaks up the idophor (and then eventually the alcohol) I would suspect most bugs, whether microbiological or literal, would die off. I also wouldn't fill it with anything expensive for the first time using it, just in case.
Or wait for better advice, I'm essentially just bumping and subscribing to the thread, lol. Good luck, man.