Toilets, Sinks, Showers, Tubs and Disposals - Crack in plastic bathtub

Live in a mobile home with plastic tubs. One has a crack in the floor. How can I patch or repair the crack? I can't afford to replace it.

You're not going to like the answer. Any repair you make will just get you by until it can be properly replaced. Can you access under the tub from outside by removing any panels? If so, you can use spray foam under the tub to fortify the installation and keep the bottom from flexing and re breaking. Once the bottom is supported, you can use a fiberglas repair kit to patch the hole, sand it down and spray it with an epoxy appliance paint. Let us know what you will be able to do.

Those bathrtubs are REALLY cheap, thin-walled things. Have mended these okay with Goop you can buy at big box stores. Neighbor also borrowed my Goop and successfully mended fissured cracks around tub drain hole as water had been pouring out onto the ground. Goop (which is totally clear) is more thick-bodied than epoxy, so it builds up better. Something like epoxy putty stick may also work, but then you'd have to paint as already stated.

IF tub is pvc, you can find piece of flat pvc stock and literally fuseweld permanently on a patch, if looks does not bother you too much. You'd want to round/bevel the edges and/or ramp up the edges later with Goop.

How can you tell if it is pvc?: Use pvc primer or cleaner and put some on cracked area. Then try to scrape. If it starts to scrape up and gather material like carving into a bar of soap, it is pvc.