My simple brain looks at the whole frame bending thing in a much more simple way. An RV trailer sitting on dual axles is going to have 6-8-10’ hanging out past the rear axle. The weight supported by and spread over four suspension points on each side. And the weight of the RV is going to cause that rear cantilevered overhang portion to sag downward.
Now put jacks near the rear of the trailer and raise those jacks to level the trailer and that new upward force at the rear is going to start taking weigh off the suspension, and instead transfer that weight to the rear of the frame. Now the center of the frame with less support will tend to sag downward due to the transfer of points supporting that weight.
Lift at one rear corner more than the other and the frame will tend to twist.
What is wrong with that simple view point? Doesn’t need a discussion of gravity.
