The Royal Guard has a short window of usefulness, and is best used when the turrets are very spread out and cannot concentrate fire on him.
My top suggestion, actually, would be to upgrade to HQ6 ASAP. The extra transport and armory change the game so much. You'd immediately be increasing your total loadout capacity by 40%.
Also, bite the bullet and upgrade your hero command to lvl 5 soon. The Elite AT-AT is the best hero the Empire has, especially when you unlock the AT-ACT equipment, which I was able to quickly do last week with the grind crates.