Definitely make sure you get a decent one. I had to redo the bands on mine, since it wasn’t water tight (copper nails are great). The charring on the inside does a lot to limit rot. Combined with the aged oak, it’s been quite resistant so far.

I would also recommend sticking a metal spout near the top. Mine is fine until it overfills, then I can get a lot of algae growing on the top bit.

Fyi, an old whiskey barrel make an excellent rain barrel (at least for gardening). A half barrel underneath acts as a stand. They look a lot better than a plastic barrel.