I have a built-in vanity with double sinks in one bathroom. There was a leak in the p-trap that went on for quite a while. It soaked through the floor of the inside of the vanity and has warped it. I'm thinking that to replace it with some plywood, I will cut the floor out with a jigsaw leaving a ledge around the perimeter. Or can someone who has done this before suggest a different method?
Just like you plan, but maybe add a center support system, criss cross 1x4's under the bottom. No easy way to do it. Other option, besides replace while vanity, remove the vanity and slide the old bottom out and slide a new one in.