All of the sea weed products really "come to life" when you use envirotex or other glossy resins to add that super wet look. I just spray it down with a clear gloss for a beach scene and use thicker resins for underwater looks.
The "Seaweeds" have been designed to stay flexible. They can be easily glued (superglue gel) to a base and because of the flexibility, conform to different shapes such as rounded rocks.
The rigid habitat products such as the Lotus pads and Eel Grass can easily be modified to add contours and re-shape them by heating with a hair dryer. (WARNING; Heat Guns may melt material or bubble paint)