Hi Ron, had the same problem with my 8'-6'' HMS Fearless when I first launched it. Took out all the ballast, weighed it then replaced it with a solid steel keel on edge bolted to the underside of my boat.... cured and never any more problem since. Fast boats go past it and it sits still with the wake going along side, just like the real one. it gave the boat a stabilising keel and put all the ballast 60 mm lower than being inside the boat. Good luck with yours, interested as to how it turns out.

Think a bilge keel should be the first step. My next suggestion would be to add some of the ballast to a removable fin keel, bolted to the underside of the hull. This will increase the righting moment, but not the weight. This can be seen if you examine U Tube videos of cruise ships and liners. They have so much superstructure they are inherently unstable.
Have built several freighters and always fit captive nuts into the keel or underside. These are intended for trunnion display mounts, but have always been prepared to bolt a keel on if needed. The nuts can easily be sealed when sailing.

https://www.marineinsight.com/naval-architecture/roll-stabilization-systems/amp/

I chose to add a bilge keel to begin with in the search of stability.

you could consider using some of the modern tech and fitting active stabilizers there are a lot of cheap solid state gyros and if your receiver does not have enough free inputs and outputs an arduino mini could handle the logic.