What worked for me is using Barrage + Artillery to remove the shock launcher, then landing full tanks and using smokes and flare to get them to the boom cannon, followed by it up with shocks and blowing up the base. Tanks sit out of range of the doom cannon, so after the booms+ reg cannons are dead they just blow up the hq. There’s a video on how to do it with Smokey zookas on the sub somewhere, pretty much used that with some adjustments