Hi all! I am building a dust bath similar to this picture. I am also using that clean roofing material to cover three sides of it as well. However I want to know if I should screw in a tarp or some sort of bottom to keep water from leaking underneath it and wetting the soil in the bath. I’m not sure what the best way to water proof dirt could be. Should I make a wood bottom? Any advice is appreciated! Thank you all!