I've had my sewing room in our basement for 20 years now. I've had water in it once.. YIKES!!! but since it is just concrete and we had everything up off the floor it didn't hurt anything. (Just scares me when we leave town)
Like others I do run a dehumidifier down there from this time of year until fall.. I have my fabric down there, and my machines are down there as well.
I love it because no one wants anything down there including the space.. so I have LOTS of room and I've never had any problems with musty smells or anything like that. I use task lighting because the gray walls suck up the light. I love it down there.
I can work on a project until it's finished without having to clean it all up every time I stop sewing! I tried an upstairs bedroom, but there just isn't near enough room, so I went back to the basement.