Good question! I had the same thought, but in reality it don't move that much, about a quarter of an inch up and down when empty or loaded, like a shock absorber really.
I bought my first Engel in '97, it was secondhand, came with the suspension and the outer cover, cost£500 back then and secondhand! It ran for years and years then it packed up, bought a new one for not much more, kept the protector and the suspender, now fitted properly, it's not something I'd go and buy, but I had it already.Bill Westley