My father passed on a numbr of years ago, I remember the day and everything that happened that day very well. He taught me to shoot and hunt and gave me my first guns, a Mossburg .22 semi auto rifle and a J C Higgins single barrel 16 gauge)for 2 different birthdays), then later an A5 Sweet 16. You will always remember the good times with your father, which is a good thing. You are fortunate to have had him for a good while, mine was only 55 when he passed on. May I also offer my sympathies on your loss.
I solved my problem of not enough space in my safe (unrelated to the above story completely) by buying a Browning vault door and building a reinforced concrete vault room in my basement. You can make one as big or as small as you want, the same door works just as well on either. Mine ended up about 7' x 6' inside dimensions, plus an offset of 3' x 3' which I shelved to hold my ammo. I use a dehumidifier made by RCA Whirpool, bought it at Sears, the discharge line is connected to the house plumbing system in my crawl space area, and it works great. I lined the rough concrete walls with a commercial carpet with a rubber backing on it, that prevents an occasional bump of a barrel from doing any harm, and looks great. I carpeted the floor with a RealTree pattern commercial carpet, and installed celotex ceiling tiles on the underside of the reinforced concrete ceiling. Everything together cost me only about 2 grand or so, (several years ago now) using my labor with help from one of my sons. It would take a jack hammer and a good bit of time ( and a lot of noise) to get into it. As much as you fool with guns you might want to consider something similar.
