Am I insane?

Screw it go for it think the only thing holding you down is cost of materials and machining especially if you're adding a message to it, if its just an artifact/statue you're shooting for maybe opt for a more budget and workable material than tungsten. Some kind of industrial metal you can work with like steel or even aluminum may be a better alternative stone material (granite or marble) being the best IMO for longevity, encase it in epoxy and then put in a PVC pipe with desiccant for added measure. Finding a location where it won't be disturbed is probably the hardest part of this. Can't be exposed to UV light or harsh chemicals, so ocean is out (think its illegal to dump there too). If burying, it needs to be below the frost line for sure in fairly stable ground, with good chemical makeup of the soil, where people won't interact with it. I personally can't come up with a legal means so you might have to get permission from some kind of protected grounds like a national park or something. Even then at most it will last maybe a couple thousand years, longer if using stone material instead of metal