Have you thought about putting down rubber "jig saw" tiles that interlock ? supposedly they are good under a longarm and frame. They keep down noise and vibration. They are super easy to keep clean, you can damp mop if you want. They're comfortable to walk on, and they also insulate a little. If you do have a water leak, they are easy to take up and dry out. They don't absorb much water. If one gets damaged you can just replace it. They are 2'x2' squares and they cover a large area quickly. The Depot stocks them usually, depending on the size of the store, but if they don't stock them they can special order them. They also stock or can order different colors and designs, you can make a really neat floor. They also have another product designed for garage floors that works on the same principle, that is a harder composition, that is nice. If we didn't already have carpet in the room our longarm and frame is going in, it's the way I would go.