Can anyone explain why you think a body on frame is better for towing when compared to a uni-frame? Ive never heard of either failing.... Technically the uni-frame used on the WK is more ridged when compared to the body bolted atop the frame...
The 3.7 is no power demon. I have a liberty with one and routinely tow with it.. Its not fun... Not much low end torque, it has to downshift a good bit if you want to maintain speed.
The MB transmission is a good transmission, it may be matched to the 3.7 better than the transmission is that Jeep used in the liberty. The MB tranny is a 5 speed transmission with a lower 1st gear ratio then the 42rle (in my kj) and the 545rfe used behind the 4.7 and 5.7 engines.
You'll have no issues pulling the boat up the ramp.