Removing Second Plain text Cookie

A quick search here on DevCentral for 'irule cookie removal' should provide all you need, however...

If the DMZ F5 only has one pool member (the inside F5's VS) then surely you don't need to configure persistence of any kind on that device as it is unnecessary? That being the case you only need to encrypt the cookie on the inside F5. You should be able to do that within a HTTP profile rather than resorting to an iRule.