I do quite a bit of venison sausage and I would highly recommend increasing your fat content. If you can find mostly fat pork trimmings you would be good at 70/30. Most pork butts are too lean unless you go to 50/50 or higher when mixing with venison for many sausage styles.

Anyone have firsthand knowledge on the prevalence of trichinosis in bear meat and how to handle it while processing?

In my experience, you will get fat on the outside of the casing when the core temperature of the meat gets much above 160 F. Monitor temperatures closely and pull the summer sausage out when you reach a core temp of approximately 153 degrees F. A cold water bath after they come out will help.