If using satchels, I'd be far more inclined to use bubble wrap instead as the peanuts will shift in transit and expose the item inside to possible external damage.

Agreed. What I generally do to take advantage of satchel rates and keep items well protected at the same time is wrap the item once or twice in bubble wrap, cut cardboard to size and then tape it to the wrapped item so that it's boxed in, then fill the void of the satchel with other padding (peanuts if I have them to hand, shredded paper if I don't).