Assuming that you already configured SSH settings and that script works fine from terminal, using the keychain is definitely the easiest way to ensure that script works fine in crontab as well.
Since keychain is not included in most of Unix/Linux derivations, here is the step by step procedure.
1. Install the package:
2**.** Generate keychain files for your SSH key, they will be located in ~/.keychain directory. Example for id_rsa:
3**.** Add the following line to your script anywhere before the first command that is using SSH authentication:
I personally tried to avoid to use additional programs for this, but everything else I tried didn’t work. And this worked just fine.