I'm soon to embark a wooden playset for the kids. The plastic slides cost a small fortune, so I am toying with the idea of making a wooden slide. I figure I could set 2 2x8s like stair stingers with some bracing perpendicular every foot or so. Then use MDO, PVC trim, or some other plastic/ wood compostie trim to make the slide surface. Thoughts? What material is the slipperiest and can withstand the outdoors.?