Grease the crock of the slow cooker very well.
In a bowl, mix together the cake mix, apple pie filling and water until well combined. Spread evenly in the crock.
In a small saucepan over medium heat, stir together butter, sweetened condensed milk and evaporated milk until well combined. Bring to a boil, stirring often, and then pour over the cake mix in the crock.
Cook on high for 2 - 3 hours, until the top springs back when lightly touched. Turn off, remove lid and let sit for 15 minutes.
Run a knife along the edge of the crock to loosen the cake. Invert the crock over a serving platter and let the cake drop out. Spoon any remaining caramel sauce over the top of the cake.
Serve warm with vanilla ice cream.