What I am trying to prevent is to have a collection of "important" numbers in plaintext on a laptop, which will be moving around geographically and susceptible to theft.

A salted hash is a good way to make sure that these numbers are not stored in plaintext - and it is easy. The issue is that I will eventually, in a secured location without network access, need to reverse this hash (hence a rainbow table).

The laptops are already using full-disk encryption, but this provides only a single layer of defense against exposure - I am thinking about how to add another layer without doubling the number of passphrases to remember (or forget).