Only full length UQ's, especially when you have to set up tight, have a tendency to pull away at the crease (which is usually where your butt is).
And as far as sliding over, should just be a matter of tightening and loosening the suspension on each appropriate side but something I did with my incubator was through shock cord on the sides of the UQ and over the ridgeline and cinch them up. Kept everything close and in position. Purpose for the tabs Adam put on the incubator.
"I ain't here for a long time, I'm here for a good time"
- George Strait