Sagging in cab-over bed area -> how bad is this?

I wouldn't head south if there is any question. There are only a few roads in Mexico that are as smooth as any paved road in Texas. The roads and topes(speed bumps)there can really take a toll on campers. On our first trip with a wood framed Hallmark we almost lost the battery box. Our current Bigfoot is riding on an external steel frame I built when one of the frame beams started coming apart causing a sagging floor. It is 11.5 feet long with just too much overhang.