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.
Chain should alway look 'wet'
use Motul chain lube, its nice clear stuff.
Trolley jack under the rear linkage (Ive a bit of rubber on my jack) to lift the wheel slightly... (if you dont have a race stand, or someone to lean it over for you) while you spin the rear wheel and lube 2 revolutions of the chain.
Best to do it at the end of a ride while the chain is hot.. it wont fling off so much next ride.
A properly serviced chain takes something like 15% of the engine power... a poorly lubed/stretched/overtight one robs heaps more.