oversteer/wandering on van conversions/ class B?

I have a 1997 Xplorer 230XL on a Dodge chassis. It wandered a lot for 2 reasons: the front axle is 4" wider than the rear and the rear tires are inside of the front tires tracking. When I added rear axle spacers to even up the tire tracking that made a difference. Then I replaced all the ball joints and that tightened it up.