Have you heard the one about the $0.25 part that grounded the million dollar plane?
Try this stuff, AKA plumbing tape, from any decent hardware store or department store with plumbing fixtures. Water is kind of its job: http://www.saltysupply.com/product-p/rfp1213.htm?gclid=CILLor6AzsACFWwQ7AodnBAA5Q&CAWELAID=120129870000145341&CAGPSPN=pla&catargetid=120129870000142725&cadevice=c
You can also use double-layers or triple-layers around the rim of a bucket to help seal it.
If you go with PVC, you will either have to break it to open, or still need the tape or another sealant in the lid.
Unless you trust the bell method, but that requires you to go underground or underwater, and for the water table to never drop below the lip.

Search geocaching for other ideas as well. They're good at it. But remember that in 2-5 years, Mother Nature can make big, big changes, so don't count on just a couple of trees or rock to tell you where your stuff is if you go under ground. Plus, if you need the cache, you have to have a shovel or at least an ax or hoe to get to it if it's buried.
They grow, change size (and with buried tubes, a foot or two off makes for a lot of unnecessary digging), push stuff around, get cut down or hauled off or sometimes end up split from a limb or strike or other humans and hiding marks that were made as guides.
There was also one freak accident where the boy scouts were unable to retrieve a box for the next coordinates because no-fooling a tree fell over on the spot. Like, a big one, and the park people said we couldn't go get a chain saw. That has to be a once-in-a-lifetime thing, though.

Good idea's. 🙂 I was a little concerned that there would be a forest fire. A stump made outa cedar wouldn't have lasted long.lol
The whole idea of the Mossberg tube was to be able to burry your guns if there was a clamp down on firearms from the Gov.
Good thing I didn't rush out and burry a bunch. Looked like an awesome system but looks can be deceiving I guess hey?

The article says :
PVC TUBE: They’re easy to seal completely shut to protect from water infiltration.

Not sure how he is meaning to seal them shut, and then how do open it when you need it ?

Good idea's. 🙂 ...The whole idea of the Mossberg tube was to be able to burry your guns if there was a clamp down on firearms from the Gov.
...

Are we talking about the Mossberg JIC/Just in Case kit?
Yours might have experienced a user/manufacturer error along the way, and it might be worth contacting Mossberg to see if they'll send you a replacement for just the tube.

Those things are all supposed to be waterproof to 40 feet down, and two of them are supposed to find the surface and float (not sure about the non-green or non-orange ones; the orange one is not quite good enough to be a flotation aid for 250# even mostly empty).

A buddy has one (wanted the finish and configuration, and it was actually the cheapest way to get it) and we stress tested it in freeze-thaw conditions at varying water levels and coverage, and it held up like a champ. The kit with it ... not so much.

Goldie:
PVC can be sealed by gluing on an end piece that's either a solid cap, or gluing on an end piece that's a female-male connector. The connector then fits to a rounded termination cap or a flat, flush-sitting cap with a little "handle" of sorts that sits up.

To ever get the two types of caps off again without cracking the PVC but to make them water tight, you can use several products inside the threads. Depending on the quality, grease can run if it gets hot. Some aerial chemicals can also cause grease to change a little bit and ruin a seal. Or there's cheap no-adhesive plumber's tape that you wrap around top to bottom.

The tape is the same stuff you use to fix a minor leak in a faucet thread, or sometimes in conjunction with other pieces to patch a leak in a relatively small pipe.

If you have big, strong hands or fresh PVC and a pair of mobile vises, you can get the terminal end cap off. The flat cap is meant to be twisted on and off by hand, but leverage and friction sometimes help.
If the PVC is old or weakened from exposure, especially light, you can break it pretty easily.

He may also mean to just glue them, then use a rock, heavy wrench, hammer, hatchet or shovel to crack it open, although fresh PVC can sometimes be resilient and sometimes cracks like an egg, depending on the wall thickness.

Yes MrsPrepwPets..
That's exactly what I'm talking about and yes it is a JIC kit.
I have the orange one as well but wont be trying that one after the bad experience with the green one.
They are both the same and I don't want to risk it.
I will try the simple tube cap and glue method..I have a geocache GPS unit from Garmin. Will have to try it out..