Here's a look at a prototype motorized trailer sent to me today and it's attached to a PNC Pico Dolly. Still a prototype, it's supposed be universal and have some mounting options to attach to several different dollies or maybe even sliders? The idea is to have a motorized push cart to have consistent movement all of the motors, batteries, wiring, and switches all self contained into one little unit.
There's a few 1/4x20 threads to mount other accessories on the little push car too. From the image it looks like it's around 4" wide. I have no additional information about availability or pricing at this time. What do you guys think about something like this? For more about the Pico Dolly, you can find that information at the following page: http://www.photographyandcinema.com
Pico Dolly from PhotographyandCinema.com