I am trying to decide between the Mariner 3 and Mariner 4. The size and weight of the three make it attractive and I don’t need all the space the 4 provides. My concern is the 3 only has 2 tubes while the 4 has four tubes. One of the reviews read think Titanic with an inflatable. How big a problem is the two tube design and does it make the Mariner 3 significantly less secure?