I'm with Brian - if you wait to see rust, it's too late.
When you come back from riding in good weather, take a minute to inspect the chain. If it looks or feels dry (no lube) - lube it. Because of the wet weather you'll have to do that at least once a week to keep it from rusting. Don't forget to hit the backside of the plates as well.
I use a wax lube that goes on wet and dries to leave a light wax film. That's about all you need. You are preventing the plates from rusting and lubing where the rollers contact the sprockets. The rest of the chain is lubed internally.
Jay