I have seen vertical tanks on their side and work...never done it myself. I will say that I would never, ever, ever, ever bury a pressure tank. I know a lot of folks do it, but to me, it's the dumbest thing in the world to do...it is something with a relatively short service life and in my opinion should always be accessible. I've refused jobs before where people wanted that done. If you have constant pressure, put in a small tank above ground under your fake rock I think I see.