You wouldn't need an inverter to power electric heaters. If you build your own heating system they can be run off 12v d/c. saving you the cost of an inverter. Many people use electric heat for their dump load, or in your case to use the wasted PV capability.
As fas as saving money, you would be better off though using your stored electricity to power your a/c loads (or replacement d/c appliances) vs using the power for heating. In most places, the energy contained in natural gas is far cheaper and more efficiently used than heating by electricity.
List of good uses for your RE power would include anything that uses a wall wart, lighting needs, low power a/c devices. Of course having both a/c wiring and a d/c wiring system throughout the house would also increase your costs for wiring them.
As far as running your frige it does sound as though you have a system big enough to do so, however "10 panels and a dozen marine batteries" isn't enough information to go on, they could be 10 w panels, or 250w panels charging a storage system of any size.
You would need to know the surge wattage of your refrigerator, and buy an inverter of pure sine wave( modified sine wave inverters do not run motors very well) large enough to handle the load.
One way to keep the system simple is to purchase grid tied inverters that also have the capability to keep a battery bank charged and can be disconnected from the grid in the event of a power outage. This type of system, however is probably the most expensive option.
