It appears the compartment is enclosed so you would just need to put one of the personal 250W heaters in there and plug it in. It will warm everything up pretty quickly. Since it's only 30 degrees outside it should not take long to thaw things out. Be sure it's well sealed and give it as much time as possible.
You may also be able to install a cap like this
http://www.campingworld.com/termination-cap-with-hose-connector on your output connection and blow water backward up the discharge to free up and blockage. You need a hose with female connectors on both ends but it does work.
