Shotgun scabbard -> depends - if the pack has side compresson straps you may attach the scabbard to those and it should hold just fine.

As for tent - Depends what you wanna do and what sort of tent
you have. I stuff my hammock or solo tent in my pack, but its small. with a big thang you might strap to outside, but there
really aren't any hard and fast rules. I generally avoid outside the pack for the danger of losing gear, but not always. Just do what makes sense and is comfortable.