Quoted from wanthaneeThis way your food doesn’t touch the painted inside surface. When you put the glass dish inside the crockpot, make sure you put water inside the glass dish as well in the crockpot so it doesn’t dry out during cooking. The only drawback is that the glass dish will be smaller than what you would normally have to use in the crockpot. This limits the size of the food you can put in it. You may have to cook in smaller portions.
This link is just a sample of the glass dish that I use inside the crockpot: