Many have done that, including me, but absolutely not necessary. Search here for ’LavaLock’ will keep you in reading material for the weekend!
Welcome, and it looks like you selected the wrong grill owned for your profile. The RT-680 was the first version of the Bull, later replaced by the RT-700.
Not necessary and I don’t think it really adds to any insulation value or smoke flavor. For me it was more of preserving the outside of the grill from smoke stains.