I have never even thought about that one. Perhaps if a padded gun case is available that’s long enough, bungee cord it down with one on the front rack and the butt stock on the rear rack. Might want to putt a little padding on each rack.
My Crockett rifle isn’t all that long so I just lay it across my lap or hold onto it with one hand IF I’m on flatter ground, which is scarce in this part in this the world. One thing is for certain, laying the ML across my lap and riding a 4-wheeler in the mountains is far from ideal. Just too darn steep here and it can cause problems at times.