I dont think there is any way, regardless of how you send them, to receive packages other than everything funneling into the postal service there. The postal service in Guatemala is the problem. I worked in the mission office for a while and that was the only way to receive anything for anyone in the mission regardless of how it was sent.

Its just the name of the game to have things opened or lost. People suggest plastering the packages with pictures of Jesus, Mary, etc, but I almost think that puts a target on them.