Mitch, take a look at this: https://www.flickr.com/photos/moribundworld/8962444804/
Something I made in June. Uses a macro slider as a rail and I can assure you it is rather steady. The cost is low and if you get a spring back, you'll need minimal woodwork. You only need bellows and spring back, rest is simple hardware store stuff and the rail comes for approximately 15€ shipped and has a tripod thread.