Angling the wheels slightly outward would at least work to course-correct if the weight of the contraption gets slung out. If the car leans left it'll have the

Angling the wheels slightly outward would at least work to course-correct if the weight of the contraption gets slung out. If the car leans left it'll have the most weight on the left-angled wheels, putting it back on all four wheels. The mirrored situation happens if the car leans right.