When I built mine I caulked the inside edges then I painted it with boat paint, which I think is epoxy.

I did about two coats of paint and that was it. I've had it for three years and it works fine.

Make sure you you have an angled towads the drain, and you should be fine. Remember it's not a bathtub, it only has to direct the water towards the drain and out.

Michael McBlane