They make a vertical gun holder. We used them on golf carts for sporting clays. If it’s close to the tire and not in a case it’s going to get full of sand, mud and anything else you ride through.
the only good solution I've ever found is a scabberd mounted on a kid trailer. When I don't use the kid trailer I just have it on my back. I've tried to mount scabberds on the bike and nothing has worked. I don't like handlebar mounts because bikes fall over. I like my gun way too much to bash the stock or barrel into things at speed.
I'm still a rookie but I found everything on my back worked best. Even my bow. I definitely did not like my bow on the handle bars, at least the trails I was taking.
It would probably work. I've never tried exactly that but I have bungee corded my bow to my backpack. I usually just use the bike trailer though, mostly because if we get anything I will need it anyway. My personal pet peeve is having to go all the way back to the truck just to get what I need to haul game.
