David, I haven't use Rhino liner, but I have used a 2 part urethane product on inner fenders, floors and other places I would normally use undercoating. I got the kind that you mix the texture in with the product prior to spraying and left the texture material (ground rubber) out for a smooth surface. I really like the way it turned out and it's wearing like iron. It washes off easily with a high pressure hose (car wash) and still looks good even after some miles on gravel roads.

In my opinion it definately beats paint or traditional under coating. I'm not sure aobut the leaving an edge for water run off, to me it would seem the smoother it is the better the water will run off. I never thought about getting it off, but I think it would be a real PIA.