The payload ratings for the trucks keep rising every year. The new SRW trucks can support weights not considered even just a few years ago. I know there are many on the Montana Owners Club forum that do tow the larger Montanas with SRWs and say the weight is within their new truck ratings. And they say stability is no problem either.
I pull a 35' Montana with my 2012 F350 SRW. It is within the weight and tow ratings. It tows the 5er great and stability is also great, even in strong cross winds. And pulls Colorado mountain passes with little effort.