I'm anything but an expert...but I think your dog is in danger in ANY box, crate, in the cab etc because they don't wear seat belts. I picture them in there looking like four legged crash dummies in a serious collision. I wouldn't want to bounce off the wall of a houndsmen at 50 mph. They LOOK a lot more professional than mine, and if I used mine all the time I'd have one or build one myself.
I have a plastic one for now with the mud river cover...I feel like that mud river cover strapped down will keep my dog inside and some what cradled like a straight jacket in the event we make a sudden stop that throws it and breaks the plastic..I have not tested the breaking strength of that cover but I'm certain i could lift several hundred pounds with it. I strap it down with nice heavy straps right next to the tailgate. I feel like that way in an abrupt stop, that cover will be able to stretch/elongate a little without hitting anything solid. Also, I can drop my tailgate and let her out quite easily.
I really don't like that I can't lock mine though. I really like the Gunner Kennels for that reason.
I'm not trying to be argumentative, only defending those of us who roll this way. I've put a lot of thought into this. I certainly hope I never have to experience a serious impact with my girl in any truck.