I recommend Flex Seal....Hate to say it Paul, that tub is going to leak. Lol I had to remove and old cast iron tub some years back and had to use a sledgehammer to break apart and remove. Remodeled the bath room and within a year the house flooded and we had to rebuild. I paid a contractor to do the work.
After the flood in 2016 my house took on 31/2 feet of water and pretty much the whole interior was destroyed along with all the furniture. Too much for me to take on by myself. Our whole town was underwater. But then again carpentry wasn’t my thing anyway. Small stuff I can do. But mechanic work is a breeze for me.VWD, I wouldn't even know how to hire a contractor.
Hack, you have to be fast to use this tub, fill it before the water runs out.