This is from the Mobil website......these responses suggest there's no reason to change annually if you get it up to operating temps often enough to burn off moisture;

Question: How to Handle 20,000-Mile Motor Oil Drain Intervals When a Car is Driven Infrequently Porsche recommends an extremely long drain interval of 20,000 miles for Mobil 1--which is great but since my 2006 911 is a "weekend car" it only gets 5-6,000 miles per year. Should I wait to change the oil at 20,000 miles or should I change it when 2 or 3 years are up?-- Roy James, Phoenix, AZ
Answer:
We recommend following the drain intervals listed in your owner's manual. Mobil 1 would satisfy those longer drain intervals as long as the manufacturer makes that suggestion.

Proper Change Interval to Avoid Moisture Buildup in Infrequently Driven Car

Question: I have a 1988 Chevrolet Caprice Classic Brougham LS with under 70,000 miles. It's a 4-barrel carb/5.0 V-8. It's been garage-kept its entire life in showroom condition and driven "lightly" 2-3 times per month. I change the oil every July and January with 5 quarts of Mobil-1 with SuperSyn. The car resides in New Jersey. I put approximately 1,500-1,800 miles on each oil change interval. Am I changing the oil too much? I allow the engine to fully warm-up and reach highway speeds during its rides so I was thinking changing the oil annually. Advice would be appreciated. I am more concerned with moisture build-up over time than mileage, even though the oil is synthetic. Thank you-- Anthony Mancini, Somerset, NJ

Answer: If you are getting the vehicle up to speed and warmed up at least every few weeks, then maybe you are changing your oil too frequently. If you never got it warmed up and hot to burn off moisture, we would recommend at a minimum an annual Mobil 1 oil change. For your circumstances, annually is a conservative and safe strategy.