Do you have any slow cooker recipes for mashed potatoes and other tips for this kind of cooking?

Certainly. However I think the easiest way to make mashed Idaho® potatoes ahead of time is to boil the peeled and cut potatoes (1 ½ inch to 2 inch size diced) and drain once fork tender and then add a little lemon juice to keep from oxidizing along with warm milk and butter. Then add to a slow cooker and keep them warm on a low setting. Just stir and serve.

Here are some other slow cooker ideas for potatoes: 

Easy, Cheesy Idaho® Potatoes and Ham

Slow Cooker Farmer's Market Idaho® Potato Stew