I could certainly see a bad ball-joint causing that symptom. Basically, it probably had so little travel it wore a "step" into the ball-joint, and now with the new spring it has enough suspension travel to push past the "step" which is the pop you are hearing. At that age, new ball joints should just about be expected.
The rear spring shackles should not be be rubbing the spring, unless they are over-extended because the springs are over-loaded (again, very possible for that era gas motorhome). I would ask for at least a picture, but it sounds like the rear springs may need some help too, to address the root cause of the rubbing. That said... rubbing can also happen simply because the rubber spring isolator has broken down.
Please keep in mind that some of the best mechanics have the worst communication skills :)
