I tend to stay in warmer, drier climates. I check my caulking joints every month or so because they dry out and crack. I even use the recommended stuff from our local RV dealer. I have some dark (black spots) areas on the outside caulking seams. I scrape it off when I find it, and recaulk the area. Don't know if it is mold, or just dirt from wind/dust storms. With my own maintenance schedule, I still have dry interior after 7 years.