Sadly it has always been an option on the beach, standard on the SE and Ocean. Yes the 12v pretty much runs the lights, and any other things you attach such as phones, fridges etc.
Heaters can be retrofitted relatively easily, I had mine done with a webasto. Some of the planar heaters are surprisingly cheap now too.
You will undoubtedly have the Webasto Coolant heater which can have a remote fitted relatively easily. It can then be used for a short time as a heater. However it runs from the engine battery powered so would be restricted to about 30 mins to stop you flattening the battery. Its designed really just to warm up the engine on a cold day.
If you have hookup though its easy to use something like the Kampa Cuboid, or an oil filled radiator from mains.