The lite barrels that are usually white or blue, such as those used for animal feed or for storing water can get brittle, but the thicker, heavier constructed, semi-clear white or similarly constructed black barrels should last for many years. You can even get them for free if know the right people. If you get them from a soft drink distributor then they may smell of Coca-cola or Mountain dew, but they will be immediately usable. I got mine for free from a trucking company where they had contained gear oil. I rinsed them thoroughly before storing gasoline in them but I'm not sure I would have wanted to store drinking water in them. No issues with burying all but a few inches of them as long as you don't have to worry about freezing. Burial might even help them last longer as they will have less exposure to UV and the weather. The pit lined with crushed rock would be good, but I would put sand under the barrels, between them and the rock, to cushion them from the rock. You don't want to surround them with sand as they will need room to expand when warm weather heats them up. I would also put lawn edging or something around them to prevent someone tripping over them or you hitting them with a lawn mower or something.