Refurbishing inflatable

[We Will Two]

I recently came across an inflatable cheap and have been cleaning it up, so far looks good and in good shape.

Though the transom which is like a marine plywood needs to be badly refinished. What is everyones recommendation on what type of varnish or other product to use? I also assume I should use some type of sealer first? The boat will be sitting in the water most of the summer here in Ohio.

Thanks