We towed a 20 ft boat behind a 30 foot Pace Arrow for many years, and launched at numerous launch ramps. It's not only feasilbe, but very easy to control the boat as you back down the ramp - just use the side mirrors. The long overhang at the rear of the motorhome means that your wheels will probably be dry, and the weight means you'll have good traction on most ramps.
My only problem when launching/retreiving is my wife cant see me in the boat. I usually hang way over waving her back. Most of the time I dont even know the boat is back there when towing. As long as you have a big enough area to turn around in for the back down, theres no problem.