To avoid skin irritation on saddle straps. Secure it with a couple of zip-tie plastic straps to prevent slipping. 1/2 inch foam pipe insulation.
It's an "elevator" cart. The cart can raise and lower the platform for the dog to fit in it. I would say this was a "challenge", and here is the "solution".
Chay in New York. He is a 90 pound G/S. The 3 pics by the blue bottle are the studs and twist on wing nuts that are used for the rear "adjustable saddle straps". They bolt together with 6 bolts and it cut the cost of shipping to $25 for the same size cart going to the same location.
This is a "knock down" cart. You can see how the back section bolts to the side rails