Personally, I would not buy a used RV because there is too much damage that can occur in the first few years if they are not kept sealed up from the weather.
Depreciation means little to me, because I keep stuff for a very long time. So I prefer to buy new ( trucks, cars, motorcycles, boats ), maintain meticulously, and keep for a long time.
I don't buy stuff on a whim though, so by the time I have decided I want to pursue something as an activity, I've pretty much decided this will be something I will do for a long time.
It took me 19 months of serious looking before I decided this trailer I am in right now was the one I wanted.
To the OP, if you think you may only keep this thing a fairly short period of time, used may be a better way to go from a dollars and sense point of view.