I need finish suggestions for my project. I am currently building a wooden ofuro style soaking tub. I am using 2x8 boards or meranti wood though not sure of exactly which species. Some boards are lighter in color and weight, some are more medium red/brown and heavier. I want a finish that is going to make sure this bath tub lasts a life time.

I understand traditional tubs are not sealed however I plan on sealing this. I have heard of products called "penetrating epoxy" though I have read criticisms that they are just thinned down epoxy and don't penetrate well. Total boat makes one that seems legit but not cheap. My local epoxy/surboard supply shop said I could just thin one of their normal epoxy mixtures and use that but I am skeptical. I could just paint/pour on a counter-top type epoxy coating though it may be hard to get on nice on the inside of the box. Outside of epoxies I am not sure what would be a good idea. Polyurethane would seem to make sense, a few wipe on layers followed by a few brush on layers.

Anyone with experience on this is greatly appreciated.