I just went through the same agonizing situation. New Montana HC 318RE with a much heavier pin weight thanm my Cougar XLite. We pulled the Cougar all through the US last summer with a 2012 RAM 2500 with a Payload sticker of 2,070# I was probably marginal with that. The new 5ver would put me way over the sticker. As a result of lots of Forum threads read and posted to, I ordered a RAM 3500 Single Rear Wheel CTD. Now the only thing I will worry about is finding a hitch for the factory in bed 5th wheel prep.
Safety is a big concern and the SRW should give me about the same ride as the 2500.