I recall a story, not sure if it was true, where a guy removed the inner door panels on his rear doors on a Ram so as to get the dimension he needed for his berth. I think it also varies depending on whether your truck is a truck or a tractor. If a tractor, you can't run a pickup bed, flatbed or anything, just a hitch. When you start doing serious hotshot work, all the rules get really complicated. Like I think your trailer can only be 40' behind a truck, but can be 53' on a tractor. I think that is why you occasionally see what appears to be a really long trailer behind an F350/450/550 and it will have no bed at all. Just frame rails, mudflaps and a 5th wheel plate. But I am out of my area of expertise....if I even have such an area.