Thanks all, we actually spoke with Airstream and they said all trailers of our sort,year etc, have a weaker spot there, since it wasn't intended to have weight on it. It is actually located at the very front of the trailer, where the battery box is, and under it...our spare tire. Therefor no support was installed by airstream at the time of manufacturing. There used to be a credenza there along the front that we tore out, and there are with weak spots in the floor. They actually told us to brace it up, similiar to what you did, and that "should" be sufficient. We have poked at it slightly through the week and it seems to solve the problem. so on Saturday we will install some sort of support from the bottom/bellypan up.
Thanks for your responses, Petra and Ventura