My mother has a newish caravan with an alarm on it which runs off the battery. When in winter storage it runs the battery down so making the alarm useless. Apart from keep going back to winter storage every month and taking away the battery and charging it up would a solar panel keep the battery topped up enough to run the alarm and if so what size solar panel would you need.
Ask at a caravan shop, they should be able to help you, if not their workshop should.
Our alarm does not work off the caravan battery.
Hope this helps.