Just a caution that the entropy of length with only letters is significantly degraded when you use words. A dictionary attack will usually be able to crack a very long password if it's made up of words.

Another way to create a memorable password that is quite complex is to start with phrase, like, "Fred, the mailman, always arrives by 11:30 AM on weekdays." That can be shortened to "F,tm,aab11:30AMow."