A must have lubricant for your slide out. I apply Camco Slide-Out Lube twice a year. It protects the membrane that seals you RV and slide out from rain, U.V., etc.. It also promotes a nice quiet movement when you are extending or retracting your slide.
I don't go to much trouble prepping the weatherstripping. A simple wash job , allow to dry, spray on lubricant and let it soak in.