Trisha,
Condition is everything in second-hand value, especially if you remember a few years back when rain water leaks into the body panels made certain caravans virtually worthless.
So maybe it's not a surprise that dealers won't give you a price over the phone, but of course they have a list of trade values.
If you want an estimate for your van, compare it with similar models from the endless adds in the caravan mags.
Robert