Dear Mark :
The key item to remember that you need to define what layers your 3D contour lines are on so that RMS / RiverCAD uses them. Select Modules | Configure | Elevation Layers. From the displayed Configure Elevation Layers dialog box, define layers to use as USE, and those layers to ignore as IGNORE.
Then, to cut a cross-section from the topo map, select Input | Ground Geometry | Screen 3D Map. You can then draw a cross-section cut line on the topo map and RMS / RiverCAD will construct a cross-section from the topo map data.
I hope that this assists you.
Sincerely,
Chris E. Maeder, M.S.
Senior Technical Engineer
chris.maeder@bossintl.com