I think it should be a simple design: it has three parts: The Bottom The middle shelf (will be painted red) The lid The bottom will have a indented lip so that the lid (will use a clear material) can slide over the shelf and contact with the bottom part. Thus, the design looks like this: The middle shelf (will slide into the bottom part and be covered by the lid) It is also hollowed out inside to save on printing material. : A simple lid (will be printed with a translucent material): When I check for watertight meshes, I of course run into problems... due to the hollowed out design: Any idea on what I should do to finish this project? Attached are the SketchUp files. Thanks for reading / any advice.