Many caches are only freezedried or canned foods. Also ammo and a small gun. Oxygen absorbers are good as are also the dessicant bags to absorb moisture. Wrap metals in canvas or linen cloth, well oiled but NOT with WD-40! Too acidic. Machine oil. ammo very dry or also lightly oiled if not in the original packaging. Clothing in plastic freezerbags or ziplocks with the air pressed out. If you can get them, Mylar bags are the best, just too sensitive to cuts and punctures.
For the storage of the cache is a PVC pipe which you have sealed with glue and silicon as good enough as an aquarium!! The other end is with a gasket and a screw on lid. Place your stuff in the tube, packing close together and save space using the different form of each package. Screw the lid on well and bury the whole thing where it cannot be washed away from a flash flood, uncovered by a landslide or mudslide, not easily found by animals and dug up. Have two definite land marks where you can stand and look at them both and be standing on your cache. These landmarks should not be trees which could be cut down soon. Mountains or a special rock formation. You can also use geocache info on your smartphone or geocaching device to find it again...The last hope if your electronics die, is to have a map, drawing or photo and recognise the place again...GP
Agree with everything you said, but there are also other possibilities.
Silver/gold coins, guns, electronics, ammo, etc. can be stored in a metal ammo can. You can put in a silica dessicant and an oxygen eater to help control the environment in the can and prevent rust.
You can then completely cover this ammo can in a thick layer of autobody filler, which is allowed to harden per the directions.
This means that you now have a completely waterproof "capsule" which can be buried almost anywhere without fear of the contents deteriorating.
As to where to bury it, any abandoned junkyard, old mining camp, or anyplace else unlikley to be disturbed and having scattered metal around to confound the metal detectors. Parts of graveyards might be a possibility, as people are naturally reluctant to disturb the dead . . . and there are metal coffins and metal trinkets that people leave at graves out of sentimentality, and this will further confound metal detectors.
If you go the graveyard route, keep in mind that the authorities are aware of this idea. During the Vietnam War, many coffins, funeral processions, and hearses were used to smuggle and stash weapons from North Vietnam to supply the Vietcong who were, of course, fighting the Americans.
The CIA was aware of this, but the dilemma that this stratedgy created had to do with the Geneva Convention, as defiling graves and mistreating dead bodies is against the rules of land warfare.* It would have been a propaganda victory for the enemy if they could prove that the USA was defiling graves.
So, keep this in mind if you stash in a graveyard.
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* There are oddball exceptions that don't apply to my points. A soldier in danger of hypothermia can scavenge clothing from the dead, and a soldier under fire can take cover under a dead body to avoid being shot. There are other similar exceptions, but I'm sure you get the idea.