We just use a Dollar Store curtain. They're cheap and long enough for our set up.
An aside to the topic, one thing that we experienced in our wet bath came about when we upgraded from the original equipment "squat box" toilet to a very nice china bowl Thetford is that the bowl would fill with water when someone showered. The OEM toilet seat / lid was designed to let water run off down the sides in a wet bath shower. The new Dometic with a "house type" seat makes the shower water run into the bowl filling it. We solved the problem by cutting up another vinyl curtail to make a cover for the new throne.
Just a "lessons learned."