I have suckerbagged lots of stuff, ammo, boxes of strike anywhere matches, granola bars, things along those lines. I always double seal both ends of the bags, and have had pretty good luck. I just got thru storing a jillon topo maps and blueprints in 4" PVC "pipe bombs," but they were not buried, and I won't be around them 'til Dec to check on them. So I can't help you there. If I were going to bury something metal underground in PVC I would oil them well, maybe with WD40 or Breakfree, and toss in a lot of silica gel packets...