TIFU: I just put the fourth and final coat of interior water-based polyurthane on my outdoor bench. What's the best option to weatherproof it?

Today, as I proudly showed off the new patio bench to my wife, I noticed the can of Varathane polyurethane that I was brandishing said "Indoor" at the bottom.​All the outdoor polyurethanes I can find are oil based, and science says that those two probably don't play nice. It's just cheap pine, so it's not worth stripping and starting over, but I put a lot of work into it and want it to last at least a few years. Is there anything I can put on top to extend its life?