I have the Manfrotto 293 support and used it with my old 1-ring 80-200mm f/2.8, but I can't really recommend it for the 70-300mm VR due to three issues:
1. The support weighs 700 grams. Since the 70-300mm VR weighs 745 grams, it nearly doubles the weight of the setup. 2. The support only works in landscape orientation. For portrait orientation, you have to rely on your tripod head or add a Junior Elbow Bracket for another $70 and 320 grams. 3. The front barrel of the 70-300mm extends as you zoom. It may extend with focus as well; I can check next time I'm in the same state as the lens. But either way, it means that in order to use the support, you have to leave things loose until just before you're ready to take the shot.
So while it may not be optimal, using the camera's tripod mount may be the "least bad" option.
One of the biggest mistakes a photographer can make is to look at the real world and cling to the vain hope that next time his film will somehow bear a closer resemblance to it. - Galen Rowell