Door and window pans are becoming a requirement for new installations. There are several products on the market that can be used. The problem with these products is that they are not very flexible/adaptable. The majority are produced in generic configurations which may may only fit a small portion of manufacturers. One company, Constructor Services Inc, located in Bend Oregon, will produce custom sill pans for virtually any window or door at a fraction of the cost. The longest, single piece, pan produced to date is 24' long. Contact them for more info