Use the ruler and marker to draw the outline of the area you will cut from the front of the tub. Cut one long side panel off so that you are able to sit inside the tub.
Put on the eye and ear protection.
Cut the tub along the traced line with the reciprocating saw and carbide grit blade. Take your time going through the cast iron; allow the blade to do the work.
Sand the cut edge of the tub with sandpaper. Depending on the condition of the tub, consider sanding all over the inner and outer surface as well.
Wipe away the sanding dust with the damp rag and allow the tub to dry.
Spray paint the exterior of the tub and the claw feet. You can use contrasting colors of paint. If the tub is in relatively good condition, you can also leave it unpainted.
Cut a piece of fabric to cover the foam cushion. The fabric should measure 12 inches plus twice the depth of the cushion in length. Its width should be the width of the cushion plus 13 inches.
Fold the fabric in half widthwise, right sides facing in. Pin along the two shorter sides of the fabric.
Sew along the two pinned-together fabric sides, leaving a half-inch seam.
Turn the fabric right side out. Slide the foam inside the cushion through the open side.
Bring the two edges of the open side together and pin. Hand sew the opening together. The fabric will be very tight against the foam. Place the foam inside the tub, with the sewn sides facing the three sides of the tub.
Pile pillows along the back and sides of the tub if desired.