I have a 1/2 sheet cake in the freezer that was covered with SMBC. It's in a box which is then in a extra large size ziploc bag. When I take it out should I take out of bag but not the box until thawed. Or, let it thaw on the counter top without the box or bag.

I would take it out of the bag and let sit on counter in box. That is what i do, anyway. hth

From what I've been reading about sweating/condensation lately I would say to leave it in the bag, that way any condensation occurs on the outside of the bag, instead of on the cake. If you take it out of the bag then the moisture in the air will sneak through the cracks in the box and result in a sweaty cake... I don't know this from experience, as I don't usually use smbc, but that's the way I would do it.