Here's a quick look at the Wilderness Trail Safe backpacking holster. It's basically a padded envelope that protects you and the handgun from each other. There are a number of D-rings, and velcro straps and flaps that let you carry it a number of ways:
This holster requires a two-handed draw. One hand to open the fastex fastener, the other to draw the handgun. Velcro strips close the top part of the holster, and grasping the grip opens them up. Here's how a handgun would look inside the holster:
There is a seam that separates the gun from an open area that can take a spare magazine, or a couple of speedloaders.
The cover flap is also padded, and has a velcro closure. Small, flat items like maps, cash, etc. can be stored there.
The multiple attach points leave a lot of things to your imagination. A couple of straps, and you have a shoulder rig. That's probably a better way to carry than on the waist. Attached to a saddlebag, and the gun departs if the horse does.
One note of caution: since the handgun is completely enclosed, it is also hidden, and some states consider that "concealed carry", even if the holster is out in the open.
But this is still the only item I've seen that provides protection for both the gun and the person while riding or backpacking. It was designed especially for the wilderness.
Next topic: anybody interested in hydration packs? (For you, not the horse, unless you have a vey clever horse.)