Has this ever happened to you--or do you know a good rule of thumb to make sure this never happens again?
Unfortunately this is one of those "too many factors at play" to have one single answer. The main factors are the model/clearance of your tow dolly, and the width of the vehicle that's on the dolly. My Master Tow dolly says right in the manual to take wide turns or risk damage to the vehicle and/or dolly... I assume the damage you described is what they're talking about. I've come within millimeters (both did THAT open my eyes
) of the same thing while turned into a gas station pump, and luck was the only thing that kept my car's fender from being "creased".
Best thing to do is run some "tests" with your particular dolly and car you will be towing. Get it hooked up out in a large, open, EMPTY
parking lot and practice making turns. Start real wide in both directions, and stop mid-turn to get out and see how much clearance your car still has on the dolly. You could even measure it with a ruler or tape measure. Keep on making turns a little sharper each time, until you know it's getting too close. Pay attention to where your MH steering wheel location at that "sharpest turn you can make" point, and don't go beyond it when driving.
Keep in mind that the issue with that technique would be that it's unlikely you car's tires will ever end up EXACTLY in the same spot on the dolly ramps, every time you load it. That will change your clearance results each time... but if you leave yourself a margin or error then you'd probably be okay.