Keeping SSH open through firewall while idle

We recently installed a Cisco ASA 5505 firewall where I work. Very powerful firewall, much too powerful for our needs, but oh well. The problem is that SSH connections from the inside to outside would timeout after 5 minutes. I think this was a problem with the NAT timeout settings, but I tried many, many different options with no success on the firewall. Then I discovered ClientAliveInterval for the OpenSSH server.