I have a 42' BH Sierra, as far as what you are looking for may be a bit tough to find. I would not personally worry about whether its 50 or 30 Amps, If you are accustomed to 30A then even with a 50A rig you will be fine. I have a 50A now and have the adapter to hook up to the 30A as where I am full timing does not offer 50A service. You just have to know in your mind and actions that you cant run 2 A/C's, the microwave and washer/dryer at the same time. Keep it simple as one a/c and something else just like you would now not to blow a breaker. We have yet to blow the breaker once. If you dont mind going a little bit longer in length, we got the 365SAQ which is like a palace inside, 4 slides (2 are in the bunk house giving the kids double the room) the living room and king bed. Not bad only 14k GVWR and I tow it with an SRW, so I know you have enough truck to haul it with your Dually. Its a great family floor plan and the kids love it too.
2012 Ford F-350 6.7L CC SRW w/FX4
2013 Forest River Sierra 365SAQ