Frank, flooring isn't a weakness per se. Trailers that are allowed to have leaks
for a period of time will have rot problems in the floor, regardless of brand. I can't begin to tell you how many Airstreams have needed frame-off restorations because their floors rotted and enclosed frames rusted. Floors encased in fiberglass are a great idea until water penetrates the fiberglass. Then the flooring swells, breaks more fiberglass, and you can't get to the rot until you cut away all the glass.
Very few fiberglass RVs experience floor problems. Well maintained ones pretty much never have floor problems. Trailers that sit around for years with window leaks
do. It's just something to look for when buying used; and the older the trailer the more important it is to be thorough about looking.