Skinny Ms offers several good tips for packing meals you've prepped for later cooking in the freezer, whether they're oven recipes or for the slow cooker [emphasis mine]:
Oven Recipes - Store the meal in an aluminium pan (disposable is fine) or a glass casserole dish. Too much air in the container will cause freezer burn, so if there's a lot of empty space at the top of the container, fill it with crumpled freezer paper. Cover the pan or dish first with plastic wrap, and then overlay that with heavyweight aluminium foil.
Slow Cooker Recipes - Use good-quality freezer bags with a zipper to reduce freezer burn and prevent leakage during thawing. Load the freezer bag in reverse order. For example, a crockpot recipe might direct you to place meat on the bottom of the appliance and layer veggies on top. When freezing the meal, fill the bag with veggies first and then layer the meat on top (when it's time to cook, then, the meat will pour into the bottom of the slow cooker first). Squeeze out as much air as possible, and store the bag flat in the freezer. Freeze yummy Slow Cooker Beef Stew this week!
No matter what kind of freezer meal you're preparing, if it contains a warm ingredient, like cooked ground turkey, cool the meal in the fridge before freezing it.
In addition to this advice, the article also has solid tips on the basics of freezer cooking, which is definitely a time saver on harried weekday nights.
6 Tips to Turn Any Recipe into a Freezer Recipe [Skinny Ms]