I think the problem with the trailers is that nobody wants a FEMA trailer park set up near them. (The old NIMBY syndrome.) Today's "temporary" FEMA trailer parks are likely tomorrow's permanent trailer parks and next decade's ghettos.
IMO, the real problem with FEMA is that it shouldn't exist in the first place. Disaster recovery should be mainly the business of state and local governments in conjunction with private charities. The confusion, indecisionand waste associated with Katrina is ample evidence of why a giant federal beaurocracy should not be running the show.