I still use the older canvas panniers. After bagging the meat,I put it in a garbage bag before hauling it back to camp.Then take it out to hang it.
No blood doesn't affect performance,but it sure gets gamey smelling over time.
The Utah bags are bigger in volume,but for my smaller mules they hang down to far and put too much pressure on the rib cage. I'm kinda fussy and like to keep the packs up high so more weight is distributed along the top of the thorax.
