Shapeoko 4 Y-Axis Side Skirts

I received my Shapeoko 4 XL a few days ago and it’s missing both (W) Y-Axis side skirts from box 2. I contacted support and they said they’d send me replacements. Unfortunately what they sent are parts B & C from Box 1. How important are the side skirts? If I assemble the shapeoko without them will it cause problems? Could I add them later easily? I can’t tell what they’re made of from the PDF. I imagine they’re important for rigidity but don’t really know.