The biggest issue to watch for (and this really is a big problem if it happens) is if the butter in the caramel separates, which usually happens because you have finished the caramel but let it sit too long without stirring or transfer it to a crockpot and leave it on low for a long time. None of the caramel will stick to the apples if there is a thin layer of separated butter on the top of the caramel. If that starts to happen, it's going to take some elbow grease and a really strong wooden spoon to bring the caramel back together, but it can be done. Just turn the heat off and let the caramel cool down for a while, then stir, stir, stir, until it comes back together.