That rear-axle loading issue was why we decided to get our signature rig instead of a 31-foot Forester on the E450 chassis. Our earlier rig, a 26' Class C on the E350 frame had three ball hitches on the back, one on the centerline and two more, each in line with the auxilairy frame extensions.
The previous owner hauled a snowmobile in winter and a Harley in summer and had a single wheel trailer with two hitches that lined up with the outer ones on the RV. The trailer had a single castering wheel on the centerline at the rear with an adjustable shock absorber system that he could use air pressure to level the trailer floor.
It was a commercially available trailer back then (12 years ago?), but there may still be something similar in production nowadays. I thought it was a clever way to tow without putting a heavy bending load on the auxiliary extension frame, since the two ball joints would only transmit a "tongue weight" to the RV rather than the full weight of the bike. The single wheel would handle most of the weight.
Frank Damp -Anacortes, WA,(DW- Eileen)
ex-pat Brits (1968) and now ex-RVers, as of 08 Dec 14.