If I had the OPs rig I would do a careful inspection of my tire for cracks or other blemishes and if they appeared in good shape I would keep them for another year. Because I was under the axle and tire ratings, I would not be concerned even when my daughter came along and pushed me up to but not over the rear limit. As for being over GVWR, I would not be concerned with being 400 -700 lbs over.
And yes, I do have an RV and having many years of experience in the engineering field, have a pretty good understanding of how design limits are set risk management ??