Its age
Condition
Number of berth
Added extras
Original specification
Have a look online
Much like you would with a car, you can start by having a look online at similar models and how much they cost at the moment. Ebay and Preloved are both good places to start.
It’s important to keep in mind that some models of caravan may sound similar but in terms of mod cons and specification they could be worlds apart which therefore will have an impact on the value. Try and hunt down your exact model being sold in your area, collect a few examples of what they are selling for and then work out a suitable price based on the condition of your own caravan.
Ask your dealership
If you bought your caravan from a dealership it might be easiest to go back to them and ask what value they would sell it for now. Though this value is likely to be slightly inflated from what you might pay through a private sale, it will be true to what you might need to pay if you had to replace your caravan now.
Even if you didn't buy from a dealership, you should be able to call them up and enquire on values, most are pretty helpful.
Glasses Guides
If you can get your hands on a Glass's Caravan Guide you'll find it easy to pick out your caravan by its specific model and year. Use the Glass's Retail Value as your guide but do also consider the condition which your caravan is in