Take a look at the IGUS bag for some ideas on slides, then contact IGUS about their YES program. They are one of the incredibly generous companies that recognize the importance of programs like FIRST and can be incredibly helpful in supplying parts to build telescoping arms, elevators and other devices.
Before you do that, however, check out "Designing Competitive Manipulators" by Needel at
http://first.wpi.edu/Workshops/2006w...nferences.html
Jason