I can chime in on this. I have a 2012 Berkshire 390RB-60 with a Hydralift motorcycle carrier. I just finished a 5700 mile trip with it, carrying a 1997 Harley Heritage Springer and flat towing a 2007 Ford Sport Trac. I have upgraded front air bags and 12,000 front axle rating along with 275/80/22.5 Michelins.
The bike and lift reduced the weight on the front axle 800 lbs. to 9400 lbs and increased the rear axle weight by 2200 lbs from 17400 to 19600 lbs.
The motorhome handled no differently than before but I could see the bike and lift moving around in the rear view camera when I hit bumps, railroad crossings ,etc.