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.

x2 on caster. Too little +caster can have wander symptoms.

Ditto on front tire pressure. Mine is a 99 Dodge RoadTrek and it calls for 45psi front and 80 psi rear. I do not run quite that low in the front, more like 60 lbs. but no problem handling except in high wind conditions. Check for tire inflation sticker on front door jamb.
Bob

I have a 1999 and when the front tires are over 65 psi it wanders all over the road. when I got it the fronts were 80 just like the back, and it was quite the trip home. The wind is the biggest problem now. Mine now has 170,000 miles on it

If worn parts are not the case, have the castor angle adjusted. That is what fixed it in an astro van I had.

x2

What chassis?
I would have the front end checked. Upper control arm bushings and ball joints.