If you have hydraulic actuated slides, you have less to worry about. I agree with the comment most slides are designed to carry more weight then the slide it self. Most slides have storage cabinets and refrigerators that will be loaded when the slide goes in and out. If you have electric slides and the slide starts hang up it is either time to lube the slide or it is time for a new motor. For 50 lbs of weight I wouldn't worry about it.
2012 Cedar Creek Silverback 29RE
2011 GMC 2500HD Diesel