[CentOS] Persisting module loading

Greetings!

I have loaded a few modules:

modprobe ip_nat_ftp
modprobe ip_conntrack_ftp

And now I'd like to persist those so they're loaded when the system boots up.

I'm doing this by means of calling a specific script from
/etc/rc.d/rc.local but I believe there must be something cleaner than
that, like another existing file.

I tried the /etc/rc.modules thing as shown in
http://centos.org/docs/5/html/Deployment_Guide-en-US/s1-kernel-modules-persistant.html
but /etc/rc.modules was not being called automatically until I called
it from /etc/rc.d/rc.local

Thanks in advance,
Diogo