Your murderhole on the lower left isn't positioned comfortably for a right-handed shooter, and you might need some defense against someone just chucking a grenade through one of those gaps or over your sandbags from behind the doorway. Also consider that one can just shoot through most residential walls, so you'd want to sandbag those too, or just make a bunker like pic related in the middle of the room. If you're down to defending a room (vs. a house or whole property) you're probably fucked long-term anyway unless you have backup, so it may be better to focus on fortifying your house first and then one or more fallback 'panic rooms' defended as you suggest with comms to call for help.