A good friend of mine buried a cache about a dozen years ago.
Out of curiosity, it was dug up about 2yrs ago.
In it, was a mosin Nagant, about 400rds of ammo, a cleaning kit, a knife, and I think a couple other small items. The rifle was covered with cosmoline, and wrapped, but I don't think any other particular precautions were taken.
The container was one of those burial tubes you find online at the survival type websites, with one solid end, and one threaded end.
All items were placed inside, a small lit candle was placed inside, and the cap threaded on. Caulk sealant was packed into the threads prior to threading the cap on, and a bead was added around the end seam to the cap. It was then wrapped with usgi duct tape over the bead.
10yrs later, it was unearthed. My friends brother had wanted a mosin, so he had told him where it was buried, and that he could have it, as he was curious about how it had fared anyway. His brother took it to the shop where he works, where he and several of his friends/coworkers proceeded to open it. The tape was removed, cut off, and then they tried to get the cap off. So much sealant, couldn't be unscrewed, so it had to be cut off. As my friend told me, his brother had quite a job getting into the tube.
The rifle was perfect, just as packed. The ammo was also perfect. The knife had just a bit of darkness in some spots, or maybe small amount of surface rust, IIRC. The cleaning kit was fine. There was a spoonful or two of water down in the bottom.
I do not know it's relative depth to water table when buried, but my friend is pretty particular, I do not think he would have put it down into the water table.

Sent from my SGP612 using Tapatalk