I am sending a fanmail letter tomorrow to an actress through a production company in the city in which I live. I have two legal-sized posters I want her to sign and a letter I wrote. I am sending them through a large manila envelope, however I want to include a S.A.S.E. so that the company does not have to pay postage to send me back the posters. Can I use another manila envelope for the S.A.S.E.?