You should ask this question in the alt.rv.pop-up-trailers group. I sense that you won't like the answers you get there, however. It is not safe to tow above the manufacturer's tow rating because the vehicle will likely not handle safely, both in terms of manuvering and braking. Most experienced tow drivers keep the trailer weight below
75% of the recommended max. Remember that it is not only your own safety, and that of your family that is as stake, but also the safety of those in the cars near you if you loose control.
Safety aside, the weak link in most vehicles, when used for towing, is the transmission. It is very easy to overheat an automatic with a trailer because the torque converter stays unlocked more of the time, and even vehicles designed for towing often don't provide sufficient transmission cooling. With a manual, it is very easy to burn out the clutch, especially during low speed manuvering.
A lot depends on where you want to tow and how far. If you live in flat-land and only want to hop over to the state park 40 miles away, you can get away with a lot more than if you plan to drive through the Rockies. We recently gave up our Plymuoth Voyager in favor of a Chevy Astro; while the Voyager towed our 2000 pound pop-up fine on flat ground, the transmission would easily overheat in the Appalachian and Adirondack mountains. We took the Astro to the Rockies this year and only had to stop twice, in unusual circumstances, due to excessive transmission temperature (guage installed). I would never consider towing with my SW2, except something small like a log splitter.
I you are mainly interested in a tent off the ground, and don't have kids, then there are various popups made for motor cycles. They sleep two, and have a small space to stand up in to dress. I have seen these used by people with small cars.