I have some "investment grade" rifles and pistols, for storage there are a couple options...
The best but most difficult is to separate the wood from the metal, store the wood in a vac sealed bag with moisture controlling tabs after treating the wood with a good wax {I used vans bees wax}. Store the metal the same way except instead of wax we used a product from eezox which has worked well, have some hardwood dowels made to fit down the barrel, the dowels should be a nice dry wood and treated themselves, I did mine myself, treated with silicone sanded super smooth and then treated again, they dont have to fit super tight, some people use silicone treated fabric tubes, its just to have as little empty space as possible, also the actions should be taken apart cleaned and lubed with a quality thick oil {I use the thick wilson combat lube}..
There are a few tricks to this, 1 wear gloves when handling the guns and getting everything bagged up, make sure you do it in a low moisture area, clean them very well before starting the process, and store the sealed bags in an area that keeps uniform temperatures, you don't want the safe in an area that gets hot and cold and hot and cold, that will promote moisture..
Now the guns I have that I didn't want to get that crazy about, and I still enjoy handling, I just store them in one of my safes, it has 2 dehumidifiers, and when I handle them I make sure to wipe them down after I handle them, pretty simple in that respect, I also keep them in silicone treated socks.....
That is how a treat most of them, there are only 3 that I store disassembled, 1 is a small gauge depression era shotgun, that was never fired, I actually have the box it came in, appraised just over $40K, another is a vintage Blazer, and the last is another vintage Berretta shotgun, had this one appraised for the insurance company and they called in a third party to make sure they got it right, the value is tough to figure since the original cost 60 years ago was $30K, bought by a prominent race horse owner as a pair the other of which was destroyed in a fire, so it is now one of a kind, I was told they took 5 years to make!!! But them 3 guns are worth more than my first house so I was careful to store them appropriately...
I have a cosmoline horror story, a friend of mine went to buy a $20K shotgun and they had covered it in cosmoline at the direction of their local gun shop, lol.. They then wrapped it in wax paper {the gun shop charged them for it, lol} and then news paper, then they put it in the attic figuring it was safe, dry and away from anyone who may want to walk away with it..
Well, they pull the gun out and mice had been living in the newspaper, ate through the garbage bags the wrapped it in, and did a good job of covering the firearm with urine...
Well, they tried to clean the disaster up, and probably ended up doing more damage, my buddy didn't buy the gun, but he said the cosmoline had drastically changed the color of the stock, it was a dull finish to begin with {some of the most valuable guns have porus dull coated stocks just waiting for a petroleum product to soak in...} Someone else told me that they seen an original Kolishinkov{?} that was never coated in their grease and it was a much lighter color than any other he had ever seen...