Good shower wall covering on reno?

[Bowmans]

Does anyone know of a clear coat paint product that will seal 1/2 pine board walls so they can be used as walls to the shower? If not, how about a paint that will stick to both the aluminum curved wall and wood walls and seal it off from soaking any water into it from the shower?

Background:
We have a 1979 31' center bath AS. I am just about complete with the exterior and ready to move on to the interior. We have stripped all paneling, walls, cabinets, etc. out and stored everything for now. I pulled out the walls for the bath and left the shower pan, toilet, sink/medicine cabinet in place. I have to do a little fiberglas work on the outside corner of the shower pan and we plan on using that Retrobright to get the plastic back to original color.

My plan with the bath is to redo the walls in pine 1/2 board frames with paneling inserts except the shower walls which I will use pine 1/2 boards as the walls toward kitchen and hall. I was hoping to find a clear, water-resistant sealer I could paint on the inside of the shower walls to keep the wood finish to the inside but according to Olympic, no clear coat will work in that wet of an environment. I have come up with many ideas but they all add additional weight to these walls (aluminum, plastics) and I would rather keep it wood if possible.