Harvard wrote:
Your unit has too little caster.
Not very helpful, as the OPs motorhome is on a Mercedes chassis.
To the OP, I haven't seen too many handling complaints about the Mercedes chassis. Part of may be your expectations, depending on what they are. Although some say they do, these things don't drive like SUVs. Have you owned other motorhomes?
I haven't seen anyone mention weights. GVWR is pretty low for a motorhome this size, and it would not take a huge overload on the rear axle to make it handle terribly. I would start by knowing your weights.