You can find more information on IP Masquerade at the Linux IP Masquerade Resource that Ambrose Au maintains.
You can also find more information at Dranch's Linux page where the TrinityOS and other Linux documents are kept.
You may also find more information at The Semi-Original Linux IP Masquerading Web Site maintained by Indyramp Consulting, who also provides the IP Masq mailing list.
Lastly, you can look for specific questions in the IP MASQ and IP MASQ DEV email archives or ask a specific question on these lists. Check out Section 7.5 FAQ item for more details.