If you're up for one more suggestion, I have a 32' Southwind and found it to be top heavy also. On the highways, passing trucks would cause me to rock back and forth as well. My only difference is that I'm on a workhorse chassis with the 8.1L V8...
I started travelling with a full fresh water tank. In my rig, the tank is perfectly centered front to back and side to side, and that extra 320 pounds of low weight has really changed the ride. It's much more stable, and rocks much less. The extra weight hasn't dropped my gas mileage, and most importantly, my wife is much happier!
Best of all, it isn't expensive.