If you're intending to tow something, you want the longer wheelbase length and shorter rear overhang length.
Generally, motorhomes are typically built with the rear axle too far forward anyways (they extend the rear frame too far, rather than using a longer wheelbase chassis), so pick the longer wheelbase length, regardless of towing, and the motorhome will handle better on the road.
The only trade-off is that a longer wheelbase length makes for a larger turning radius when manuevering in tight places.