Another point on EWs is to avoid, if possible, having it wrapped up into the financing on the trailer. Get the dealer to write it up separately and pay cash (Credit Card if you pay them off monthly) for it.
We took one on the current trailer because it makes my wife more comfortable (the trailer is an orphan; Glendale went bankrupt in 2010) and since she is a worrier, silence is worth every penny we paid for the EW. It was written on a stand-alone invoice and she wrote them a check for it.
We took the dealer's financing to get a $2500 rebate on the price and then paid off the loan with a cashier's check on the 91st day, but that is a whole different discussion.