Soak your casings and add vinegar to your bowl, like a tsp.; it will help tenderize them so they're not so tough.
Also, buy good casings. Cheap, hairy casings downgrade great sausage. I get mine at Syracuse Casing Co:http://www.makincasing.com/mm5/merch...ategory_Code=2
Soak these in a bowl or pan just as-is, at least 20 min to an hour, add a bit of white vinegar to the water.
They are all domestic casings and you can get them preloaded too at no extra charge onto plastic slipons... just pull out the center tab and load onto the stuffing horn:
Make sure you give your sausages a cold water bath also as soon as you take them out of the smokehouse; it will help keep them from wrinkling as it solidifies the fat content. Linking your sausages also helps too.