I did not use a separate hip belt. I attached it to the side of my ski pack a bit lower.
Basically, I made sure that my body (hips in particular) was bracketed by the PVC tubing.
If you look at my buddy, that's pretty much his set up, too
The asterik would be my hips. The X would extend just above the *
Once the PVC tubing was on the side of my body, found the sled to be more stable. Basically, don't have the tubes behind the body, but extending to the side of the body.
Hope that makes more sense. Apologize for any confusion.