Amazing job on getting that under suit done. I love the look of a proper cast under suit. Gets pretty hot, but totally worth it.
For the floating knee, it might be worth looking at making an elastic cuff, and then anchoring it to the back side of the knee part just slightly above the center of the knee. If you do that, it'll leave the rest of the knee seal to move around, but keep the knee armor anchored in about the same spot. It'll be a bit annoying to put on until you get it figured out, but I think it would help with the knee wanting to fall down.