I have the duel voltage system on my Rockwood and have had no difficulty towing with the heaters running with my 2004 F 150. I have not had an occasion to do so with the 2011 truck. It would likely take a strong alternator for it to keep up though and my 04 HD F-150 had a very heavy duty alternator. Not sure about the new truck but THINK it would do the job as it's also an HD model. The system of course, would not work nearly as well without enclosed belly on the trailer. There was one winter that I simply didn't bother winterizing and left the trailer running on the heaters all winter (120 volt of course).
Good luck / Skip