The used value of a caravan has very little to do with the maker, even when we sold our Avondale the fact the maker was no longer there seemed to have very little effect. Possibly Lunars as the last casualty might lose a bit more but I have seen very little evidence of that. Once a caravan passes five years old parts for any make become a problem so even the manufacturer being there still makes no real difference.
The main factor has to be condition, and to a lesser extent the popularity of the layout.