Hello Malc, Solar panels may be sufficient to keep your battery trickle charged, but they are not a real alternative to a proper charge. I agree that generators are not ideal, for two reasons, firstly, they are hoplessly inefficient at converting petrol to usable electricity (I could go through the calculations but please accept that they are at best between only about 7% effiecent and usually much worse). and Secondly they are noisey and anti social in the context of caravanning.
Alternatives could be a wind generator, or whatis more reliable would be to carry a spare battery in the car, and charge it whilst you travel about during the day. Petes suggestion of an Inverter, has some merit, but it could compromise your ability to start the car (especially if it is a diesel). Use sites with electric hookups. and will all teh above it makes sence to be frugal with your power usage, turn off items when they are not being used. Happy caravanning.