I need to know of a crack filler aka mud for drywall that wont split or crack. Polymer based?

I was told something of a polymer base would work. I am remodeling the inside of my double wide and have took down the strips of the seams at the joining of the drywall but the compound that I was told to use by a local hardware store has cracked over the winter. I followed the instructions carefully now I am back to square one. So if someone knows the name brand of a product that will fill small cracks in walls like the and not split or crack once it is painted over I would appreciate it :)