I think this is my final design. I will make a final version with round holes, but the final will have removable feet for added  height adjustment. The feet may need to be fiddled with. making screw joints is always a trick getting the tolerance, size, etc. A real engineer would probably figure that out before printing but I need hands on, get the feel of the weight of the material. And it's fun, can't watch the grass grow all the time.