I have the gutterless mount from Rhino which are made by Thule. I have had problems with these. They have come loose about 3 times. the last time I went to check them while the gear was on the car, gave the clamp assembly a wiggle and the whole thing came off in my hands, left a nice dent in the roof. I haven't had problems with these types of racks before...but I'd opt for the solid mount if you have the option.
On the left you'll see a pryde mast bag. I have 5 masts in there with the top half inside the bottom. This set up works well, you can slide the mast or board in/out while still attached to the racks, just loosen the straps.
I'd also recommend to go for slightly longer bars, makes it more useful for loading, especially for 3 boards, 2 bottom / 1 top configuration.