Ok, it worked.. sort of.
I modified the revetment shape into a berm, checked it over, converted it, and dropped it into my terrain. It even matches the color of the terrain, shadows are correct, it's solid, all sides are even with the ground. I even put it on a hill, and it looks great.
Unfortunately, the item seems to have been mis-scaled somewhere along the way, because it's 10 or 20 times the size it's supposed to be. I checked the AC3D file, and in that software, it's the same scale as the original revetment. In the object editor, however, it looks about the size of a cruiser main gun battery.
I'll experiment more this weekend, but if anyone has any thoughts, I'd be glad to hear them.
Also, modifying the revetment shape into a realistic berm in AC3D was very easy.