Cleaning up SRTM Data + Adding some noise

Ok so I have been working on the map for my Game; which includes pulling a huge sample of STRM data, cleaning it and then making some additions.

I have managed to clean up the flats (and areas below ~1000m) and they look great, however I cannot seem to make the mountains look good (they are still really “lumpy”) and i havent found a way to add some detailing to my sea floor - without destroying other parts of my map.

Using L3DT I set all non land areas to a depth of 50m (with a slope down to it); but I now need a way to add noise to these undersea areas only.

I tried using select height but cant seem to get it to work nicely, as the generators will not let me generate heights that are negative.

Anyone got any ideas, I have looked at the real world terrain example as well.

Sorry to necro but how did you get a slope around the sea floor that you dropped? I have dropped mine 30m and tried to erode the surrounding vertical drops, never get anything but the very bottom of them to slope.

Regarding your seafloor features, I think you have to rise the entire world so that your very lowest point is 0 and water level is +20m or whatever you picked.