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Masterdrago, as it stands it is not very clear how Keystone comes up with its published trailer GVWR. It seems to be unloaded trailer pin weight plus the axle ratings or the tire ratings whichever is lower. Broken frames at the pin are a known phenomenon and comparatively rare, but when they occur it is almost always the result of being overloaded at that point. some of that overloading can come from weight in the trailer and some can come from acceleration loads when the rig hits bumps or dips in the road. The other instances of such an occurance is poor construction. I have seen more than my share of broken trailer frames in or around the kingpin on the trailer. Invariably the primary reason is abusing the frame by exceeding it's design specs.
I'd use 25% of the 3791RD's OEM axle ratings as a better guide. So 2 x 7000lb axles = 14000 lb. At 25% that would be 3500 lb maximum pin or whatever your available remaining payload for your tow vehicle whichever is less. With no changes to the trailer frame or suspension or tires I would not exceed the GVWR of the trailer in any case. Using 25% of the trailer GVWR could lull one into putting more weight on the nose than might be considered safe. 4250 lbs seems high, to me, for the construction techniques used by Lippert when building Montana frames. Beyond 3500lbs (in this instance) I would be start to be uncomfortable about overloading the trailer frame at that location or the truck frame. But that's just me. I'd also invest in an air-cushioned hitch or air-ride pinbox to soften those acceleration forces especially if I was anything over 3000 lbs pin weight. Again, that's just me. Others may disagree and use different criteria and they may be perfectly viable, but there is no clear cut direction from Keystone in this area... unfortunately. Bottom line be safe.
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