We cut the back 66" x 86", batting same 60" x 80" as top; fold edges of back in twice, pins pointing inward; edges zig-zagged after quilt is tied. If the top doesn't have obvious grid for tying, make a template of an old sheet.
If your church has a youth room with a ping-pong table not in use when you meet, you may be able to use that to lay out your layers to pin hems and tie.
Twice a year we have a blessing of the quilts, displaying them over the backs of the pews one Sunday morning before delivering them. This is the best way to encourage congregational support, even if you have to start small.
Our Lutheran World Relief quilting group also delivers some of our quilts to nearby shelters.