I am making Halloween Yard Decorations for my Hubby. But Need to Waterproof them?

I am low On funds so I am using CARDBOARD. He brings home from work. I have Coffins, Tombstones, Fence, a Headless Horseman, A Witch, Ghosts, Bats all sorts of things, But NOW I NEED TO WATERPROOF THEM. Because where we live we usually have snow on Halloween or it Pours Rain all Evening. I do Not want all my work Ruined in one evening Should I or Can I use Waterproof Spray. A lady said I could Seal them with Melted WAX. and paint it on with a old paint brush.