I think that the short wheelbase and long rear overhang of your Palazzo contributes some to the tendency to wander, but it's hard to say how much.
Our Aria 3401 has more of a tendency to wander than some longer wheelbase models that I test drove. It's one of the negative aspects of having a model that will fit where the longer ones won't.
Unfortunately, the length of the rear overhang of a diesel pusher is determined by the length of the engine, transmission, and drive shaft, so the only way to make a shorter coach is to remove length from in front of the rear axle, thereby ending up with a shorter wheelbase and some degree of poorer handling.
One thing you could do is test drive some other diesel pushers with the same or similar wheelbase to find out if the way yours handles is out of family or if they all handle about the same.
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