I glue basted a large quilt recently using 2 banquet tables and an ironing board. I did have some challenges reaching parts but not shifting. I put the glue on the batting which is more stable and then lay the fabric over that. It does help to have someone on the other side of the table. I would glue a section, let it dry and then move the batt and backing to another spot on the table and repeat. Did the same for the top.
Are you putting the glue on the material or the batting? That makes a big difference for me.