To be honest Woodsy, I think you've got your foil hat on too tight.
First of all, I really do not think the looming gun control laws are going to take that shape. Might you be restricted in what you buy? Yes. You may even be asked to submit documentation for what you own, but nobody is coming to kick your door in. Secondly, if they did, I think the NWO Gestapo that you fear would be smart enough to run a metal detector over your acreage.
That being said, I think it is fun to play along. Most military surplus sites sell a wide range of cache storage supplies http://www.cheaperthandirt.com/ItemList ... genumber=5
Better yet, industrial supply companies can sell waterproof storage drums and not gouge you http://www.mcmaster.com/#storage-drums/=l04wwt
I'd say one of the biggest keys is removing as mush moisture from the storage device as possible. Rice is good for that. Then I suggest breaking down your guns, oiling them heavily and wrapping the parts in plastic or oily rags. I'd seal them tightly and possibly even over-pack them with a second storage container. From there I would look for a remote location with well drained soil to bury them. My guess is that you know of a few places that are not on your homestead and that will not be disturbed by farming or utility work. I'd say that you would want to bury below the frost line and cover with natural vegetation.
Again, I think it is a big waste of time but if I were to do it, that's how I would.