Neat idea to keep the dogs up off the ground, especially if you aren't using the roof rack real estate for anything else. With it folding down, it is lower profile than most things people keep on their roof racks too.
For folks with big dogs who rule out an RTT because of it -- I'm a big fan of not lifting 70lbs objects that squirm over my head. Our solution is to get them to do it themselves:
We've since left the blanket behind and instead use
stick-on ladder tread on the hood of our rigs so there is permanent grip for them. We like the ones I linked because they have a reflective strip so even in the dark the dogs are confident in where they are jumping with just the assistance from one of our headlamps. There are two Shepherds now in our family, and two adults and one kid, and we all fit in the tent with room to spare.