Not sure what kind of proof of diminished value you presented to the adverse insurance company but they do, indeed, owe you for diminished value. I am assuming that there was no structural damage. If that's the case, your RV has lost 10%-15% of its pre-accident trade-in value. Don't take my word for it, ask any RV dealer. I'm not telling you that it is an easy process to collect the full amount. You need a good appraisal, preferably one with multiple dealer opinions, and persistence. If you aren't pro-active your claim will go nowhere.