I had similar requirements to you, but solved it in a different way.
I got some brushed ali up/down lighters from Screwfix (around £20 ea). They have been out in the elements for about 18 months now and no sign of rust.
No dusk/dawn sensor of course, so I replaced the internal light switch with a LightwaveRF radio controlled dimmer switch and got one of their Wifi-link boxes which allows you to configure rules about on/off time.
I have them come on at sunset and off at midnight. Works pretty flawlessly. Have most of the house set up like this.
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Side note: Am currently upgrading them to work with RaspPi running Domoticz and wireless PIR sensors so when someone walks up the drive the lights increase from 30% brightness to 100% brightness for 5-10 mins, then back to 30%.
Thanks for productive suggestion. I have looked at lightwaverf stuff in the past.
Just finished installing evohome for heating and I'm liking this home automation thing