If you need to draw a closed polyline around objects or inside objects, you can run the command "BOUNDARY".
Type "BOUNDARY" on the command line (without the quotes) in civil3d, and the dialogue below will come up.
You can choose to have polyline created around any closed internal obejcts by checking "Island Detection" at 2 (default behaviour).
You can choose to only work with certain objects by clicking the button at 3 and selecting the objects to work with.
This will mean that all other objects will be ignored when running this command.
Pick a point inside the area you want to create a polyline around by clicking the button at 1 and the polylines are created.
If you need to draw a polyline around the outside of a group of objects, you could draw a rough polyline that encloses the objects, run the "BOUNDARY" command and select inside your rought polyline with island detection on. This will wrap the object in a polyline, similar to shrinkwrap.