"Easiest Hymns Vol 1" arranged and published by Wayne Leupold is aimed at introducing elementary trio texture and technique in an approachable fashion, with extremely simple pedal parts. The book was published in 1994, but to date no further volumes have been produced. It can be purchased from Wayne Leupold Editions.
http://www.wayneleupold.com/organ-teaching-methods/easiest-hymns-vol-1-leupold-arr.html
As this book is under current copyright I won't be uploading any scores. However the copyright conditions do permit me to upload audio and MIDI recordings. I advise anyone who wants to learn this pieces to purchase a copy.
In due course I will be uploading performances and MIDI files of all 15 trios. I hope this offering proves to be of assistance to any CCH members who are at the outset of their skills in trio playing.
I have used the Salisbury sample set. Registrations for each trio aim to create contrasting sounds of fairly equal power on two manuals with pedal to balance. I play each tune twice - swapping hands between parts for the second half.