acs - Yes, Mason jars would make “meat tubes” or extra large sausages without casing. (Wide-mouth to facilitate slipping the meat out of the jar.) Foodsaver sells vacuum adaptors for regular as well as wide-mouth jars.
Important: The foodsaver adaptor is for post-conservation only, of course. For sous-vide purpose, a Mason jar lid & ring should only be tightened until your fingers meet a bit of resistance. This will allow air to escape during cooking.
Note: Having a tubular shape also allows you to easily slice your meat loaf into perfect 3" hamburger shapes.