One other option which I had used was -

1. Perform Backups (Weekly Full, Daily Differential, 4-hourly Log)

2. Write a script that runs every 4 hours (30 minutes after Log Backups) that zips\compresses .trn or .bak files using Winzip or 7-zip utility.

3. Let this get archived on SAN.

This should minimize the Size of the Backups taken to as much as 1\8th of their actual size. Additionally, it would safeguard the files within.

Hope this works for you.