Have, but not far or fast
I have bungied our 2 child trailer to our roof rack for short hops to our local trailhead (prior to the trail that goes 2 blocks from our house). I wouldn't recommend highway speeds unless it is somehow contained in a cargo box.
I'm 99% positive our cheap (relative) Sears rooftop cargo box is plenty big enough to hold our trailer.
I do highway speeds with bikes on the rack often, and don't worry about them anymore. They have received a few minor scrapes from bumping each other when hitting bumps in the road though.
An expensive option may be to find a small light shortish enclosed trailer (4'x6'), and pull it with your car.