There are a couple of issue that make this difficult to achieve with RailClone.
Firstly, the spline will only follow the surface immediately below it, but because of your slope, you actually need it to follow the surface some distance from the spline. The only way I can see to achieve this is to use a spline to define the bottom rather than the top of the array.
Secondly, in order to create a flat top all the way around, the segment really needs to stretch from the start to the end of the spline. In the attached file I've done this by nesting an array.
I hope that helps a little,