I use this method too after watching the Sharon Schamber tute on Youtube which I'm sure was recommended by this board. I haven't covered my boards with flannel but probably will after seeingyour tute. I've just been taping the fabric down with painters tape. On smaller quilts I spray baste and haven't had any problems but on the last biggish one I basted with washable thread. OK but the thread breaks very easily so you need to be gentle and use short lengths. When FMQ I could just ignore it which I liked very much and it did just disappear on washing. So on balance I think I'll use my washable thread again.