You don’t have to use a frosting bag, but it makes the process of filling the mushrooms quite a bit quicker and it makes them look much nicer when serving. It also helps ensure that every crevice of the mushroom is filled on the inside and there are no pockets.
You can use any kind of mushroom you prefer, as long as they are a button style mushroom, as not all mushrooms can be filled like these.
There’s no internal temperature you have to monitor when it comes to mushrooms. So no worries about that part.
I used Traeger brand cherry pellets and highly recommend the name brand pellets as I can’t tell you how much of a difference it makes. As far as flavor of the pellets, you can use any you like, but definitely use a better brand for the best results.