If you want to keep a shotgun or lever action rifle handy, but secured from unauthorized access, you might want to look at
these.
I use the rifle version of the V-line case to secure my home defense long gun. It has holes on the back side for secure mounting. Access is through a mechanical push button Simplex lock that requires no electricity. The rifle version holds up a to a 20" barreled AR-15 with A2 fixed stock, but for your needs you can probably get away with the cheaper shotgun version.
They also make a rifle cabinet that's designed to mount recessed into a wall between the studs. That unit can hold more, but is also notably more expensive, and you likely don't need to keep multiple long guns in a single location.
Additionally they offer handgun sized units, including some that can be mounted under counters. They use the same Simplex lock and can be set to the same combination.
Of course, if you go that route I would suggest keeping the j-frame on you so that if you're not immediately near your stashed gun you have the capability to fight your way to it.