The Federal Emergency Management Agency has promised it will never again use formaldehyde-tainted trailers to house victims of a natural disaster — unless, of course, it does. In a draft disaster housing report, the agency said it would use the trailers if need be, though as a last resort, and for no longer than six months. Some 500 families made homeless in 2005 by Hurricane Katrina are still living in toxic trailers. Hurricane season started June 1, and forecasters predict a good chance of two to five major Atlantic storms.