I use an old Jackass Leather (now GALCO) shoulder rig, called Miami Classic. Carry a 1911 under my left arm, two spare mag's under the right arm. Works well with tee shirt under it, and another shirt over it, or when wearing vest and/or leather jacket. Can draw it with one hand, but reholstering is problematic while riding.
I've only done that once, while riding the bike, and it was an instinctual thing, that I regretted later. I was easing out of my driveway when a water moccasin slithered across the road towards my pond. Before I knew it, my pistol was in my hand, and then I had to figure out how to stop my bike on a gravel driveway, with only one hand on the controls. This is not advisable on a 900 pound Harley Davidson. LOL Won't be doing that again.
Be safe.