If you need a good steady rest for while in the field try using a shooting stick/sticks. They can be great hiking staffs and turn into a resonable field rest in a matter of seconds. But one thing , no matter what you do, is remember this. Shoot as if you would hunting in the woods. You dont get a sandbaged benchrest out there, so practice freehand, rested with sticks, sitting....however you would be out there.
Brian M.