I've been growing toms and melons in the greenhouse in growbags for years. However, I, like Gary, up-end a grow bag, standing it on it's end, then cut the very top off, and roll back the excess plastic. I then plant 2 tomato or melon plants in the end, and train each away from each other.

Advantages .... the depth of soil is much greater. Very easy to water, and requires less watering as dries out less.

Disadvantages .... uh....