I know little about P30 other than what I've read.
1. There are a lot of front end steering component upgrade parts for the P30. That indicates to me that many P30 front ends get sloppy. I CAN say from experience that a truck with worn front end, whether Bushings, Ball Joints, Tie Rods, Idler/Pitman Arms, King Pins etc. will wander all over the road. So I think it's safe to suggest being sure your front end is tight before spending $ on the rear.
2. Henderson's LineUp is famous for their RV handling improvement skills and parts. They offer SuperSteer P30 front end parts for example. In an article on their webpage, they discuss the development of the REAR TRACK BAR. That's the part I think you're talking about for tail-wagging. Back to the article, it says one of the Hendersons was looking at a wandering P30 on their lift and noticed that there were rub marks on parts Three Inches away from the rear springs. It was that finding that contributed to the development of the Track Bar. That tells me a P30 is a good candidate for a Track Bar, just that I don't want you to work on the Rear without considering the Front.