We had a couple of small flex cracks under our vanity and bedroom slides, nothing major though. While at Twin Lakes RV Repair a couple of years ago Jay discovered the cracks while doing routine caulking and checking our roof. Jay explained that on our particular model there is a very short distance between the slide opening and the bottom panel and that a short crack can appear due to slight "flexing" of the frame. Since Jay addressed the cracks we have not had any other issues with ANY cracks! The cracks we so short I hadn't noticed them until Jay pointed them out!
Dan