Alan.
Too many unknowns.
Need year make model.
What do you and they think the current market value is?
What was the dealers repair quote?
What have you been offered?
Why do you want to buy the salvage? Do you think you may be able to do a cheaper repair than a professional without compromising your and the publics safety?
If you did do a self repair and sold the caravan on you realise you have a legal duty to tell them the caravan was declared beyond economical repair by your insurers. That is not of course the same as a constructive total loss. Splitting hairs a bit.
Do remember also if you bought the salvage, which you are entitled to do, if you make the best salvage bid, subsequent disposal could cost you a lot of money.
With more info some of us may be able to offer more thoughts.
Cheers
Dustydog