What type of slide-out mechanism do you have? Schwintek or conventional? If the former, I can't help. Call Lippert since they own the system.
With a conventional mechanism, I added quite a bit of weight w/o problems. I replaced the dinette and sofa with a full 11ft wide unit with a storage sofa and computer work station with more storage. The basic unit weighed more than the factory furniture and we stored sewing machines, dog food, drinking water, sodas, oil filled electric heaters and more.
Texas Baptist Men-Retiree Builders member since '01
13 Silverado 3500HD D/A, 2wd CCSB srw, custom RKI bed
11 Cruiser CF32MK