Agree with Y Guy that you may want to inquire on the Workhorse forum since the problems you describe are more related to the chassis than the box that Winne built.
Related to the harsh ride, if you have not already done so, suggest you load your rig for travel (including fuel and fresh water), weigh the rig, then adjust tire pressures using the tire manufacturer's load/inflation charts. If you are using max/near max tire inflation, that will transmit every bump and dimple in the road. Based on your actual loaded weight, you could perhaps safely lower pressure some, which may improve the ride. Individual wheel weights are best if you can find scales that will let you do that.