I bought a toothbelt as a sparepart from a 600 size helicopter.
It was 960mm long, my rail is 800mm so it fits perfect.
Also i bought a fitting wheel for the toothbelt and a small 380 sized gearbox motor.
I use a cheap ESC together with my arduino micro, and the servo library.
The arduino gets power via the ESCs servoline to ground and Vuu.
The minimum speed with the current setup is 10cm/min, around 80-90min for the full lenght. That seems perfect, as i can step it with pauses to make it even slower.