suspension on dodge 3500 based class B campervan

I always slowed down our PW on the 3500 Dodge chassis on dirt or gravel roads, sometimes only 10-20 mph on dirt 'cause the roads were usually rough and I didn't want to shake things up or do any damage to the undercarriage. Usually had 55psi in the air bags, about 70 in the rear tires and 60 in the front tires