ditching a C-130
I was a loadmaster on C-130's. This aircraft was pressurized, so seals aroung the doors and the cargo ramp were tight. There were exit hatches along the top so that a crew could exit the aircraft without opening the door, which would have swamped the plane quickly.
As to landing it on water, it had an essentially flat-bottomed fuselage and two sponsons, one over each main gear. I see no reason why this airplane could not be ditched, provided that it was not windy and the water was smooth.
In any case, I have personally seen a photograph of a USAF C-130 floating on the ocean. The only visible parts of the aircraft were the top of the wing and the vertical stabilizer.
At on time I had this photo. I think I found it on Airliners.Net, which has a huge database of photos.