She's probably right, but you never know. Somewhere on that site there is a link to someone who built it a little differently and brings it in the house during the winter to use as a fort. They used shower curtains with shower curtain rings to make the walls.
I say, keep the hose hooked up to it when it's being used as a fort. If the kids get mouthy or out of line, turn on the water!
Barb