try to keep it *taut* without stretching it out of shape. I've backed at least a dozen bed quilts with minkie- quilted on my long-arm. i've really never had any problems. it quilts up beautifully and makes wonderful, warm luxurious quilts.
as stated by Prism99- pull on it in both directions- find the direction with the most stretch & load it so the stretch is horizontal (side to side) instead of top to bottom- and just smooth it- don't stretch it as you roll it. make sure you are starting with a new needle- polyester's tend to dull your needle it is best to start out with a good new one. lengthen your stitch length a bit. i've used batting with mine but some people choose to not add batting feeling the minkie adds enough weight/warmth...your choice. personally i do feel that the batting helps keep the minkie from sliding around. are you using single or double sided minkie? the single sided has a smooth (polyester) back & the minkie soft side- double sided it is the same on both sides...the single sided tends to be more slippery- a bit more care is needed as you go.
once i made my first one with minkie-everyone in the family wanted quilts with it- it is such a fabulous-warm-snuggly fabric
