Still probably wouldn't be enough for 50 years and usable contents.
Ask any military operation in the world -  Something that needs to
work after long term storage needs to be in a sealed box with active
humidity control (dehumidifier or desiccant) and under pressure so any
container leaks will go out.  There needs to be active pressure and
humidity monitoring so they can restore container integrity before the
contents are compromised.

 Inert atmosphere (pure nitrogen, argon, etc.) and active cathodic
corrosion control is preferred but not essential.

 And that inner box needs to be protected in an outer vault with
positive drainage, up on a small hill so gravity alone would take care
of any water collection.  Sump pumps break, or are forgotten - it
would be rare for someone to actively monitor the ongoing integrity of
a Time Capsule, short of funding an annuity and having a legal trustee
administer a maintenance contract, things get forgotten.

 Note that the items that were sealed inside the conventional cast
iron "Time Capsule" in the same vault space have survived.  For that
small a space, a good seal, inert atmosphere and sufficient desiccant
will work.

 60 year plus old paper insulated telephone cable in underground
ducts is still in excellent working condition - because it was in
sealed splice cases, the cables are kept under 10 PSI positive
pressure with either dry air or dry nitrogen, and the splice cases are
packed with fresh desiccant packets each time they are opened.

    --<< Bruce >>--