lube slides

I use a wax based, "dry", teflon, aerosol lube for exposed stuff that can pick up dirt. Good for scissor jacks, motorcyle chains and stuff like that too.

"Dupont Teflon Multi-use Lubricant" at Lowes

This from Lippert Slide out manual (If you have a Lippert system)
SYSTEM MAINTENANCE
The
Lippert Electric Slideout System
has been static tested to over
4,000 continuous cycles with out any noticeable wear to rotating or
sliding parts. It is recommended that when operating in harsh
environments (road salt, ice build up, etc.) the moving parts be kept
clean and can be washed with mild soap and water. No grease or
lubrication is necessary and in some situations may be detrimental to the environment and long term dependability of the system.