First off the marketing term, four seasons.... and thats all it is really is really mis-leading. The coroplast material that covers the under belly, not seals.... the under side of these coaches is a just a barrier against road grime and maybe wind to a certain degree. Sealed under belly is a again mis-leading. On our last three rigs, if you tow in a bad rain storm, that coroplast will retain water like a bladder.
We live in northern indiana, and we camp pretty late in the year. One time we camped and the weather turned, very cold and windy. The key thing was the wind. We couldnt keep the inside warm running everything we had.