As a fellow sausage maker I suggest you use natural casing to make your sausages. It's your recipe and you want the best casing to complement the sausage. Stronger than Colagen, natural skin, the small intestine of the Pig or Lamb is cleaned and air tested to give the best quality sausage.
Available in 10 Meters lengths and also comes salted and Vacuum packed for your convenience. They do not need to be refrigerated for delivery as they are heavily salted. Wash away the salt with some Luke warm water before use. 
regards 
Louis