As to water penetration, we have recently weathered some heavy rain in the Carolinas with surprisingly (to me) good results. There is a lot of condensation in the trailer, but I am finding that is more due to temperature differentials and humidity than water penetration, and we have so far managed to deal with it by airing out the trailer when weather permits.
One other thought (gleaned from running cattle in the Sierra Nevada): stay away from the tall Valley Oaks if you can. They shed a lot of wood, more than other oaks, with heavy wind and rain, and their branches can be quite large and heavy.
There is some good advice in this thread about dealing with high winds. Thanks, all.