Shorter wheelbase reduces turning radius assuming everything else is equal. But shorter wheelbase also has some cons.
Ride quality can be harsher because the motorhome will have a greater tendency to "pitch" easier. Hard braking will also affect weight distribution to a greater degree -- more weight will shift forward.
A shorter wheelbase also means a longer rear overhang, which can be detrimental to towing or cross winds (everything else being equal).
There are pros and cons to both long or short wheelbase. I personally don't like the wheelbase to be so short that the rear overhang looks out of proportion.
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