Since RV's typically are not investments, they are liabilities I think the best way to look at depreciation is to assume that the coach is worth nothing in ten years. Anything you would eventually get in resale is gravy. So, if the coach is worth nothing in ten years sharpen the pencil and do the math. That should give you a realistic comparison of depreciation per year of ownership. And don't use MSRP but as others have said from the best actual discouinted price. A three year old coach ideally would have all the little new warranty aggravating stuff fixed and if a diesel should be long before any major repairs are needed. You might need tires depending on the usage from the previous owner.
I would factor in a warranty value that could offset some of the depreciation differences between pre-owned and new should you need to fix something expensive. What is the peace of mind worth to you for new tires, new brakes, new coach interior systems and a warranty? What will financing be for the interest rate between new and pre-owned? You said you would pay cash, but why not finance if the rates are low and use your savings for savings or for other income producing investments. Why tie up so much money in a huge liability? Factor all that in to your equation and the $200,000 coach that you paid $150,000 for might be a better deal over ten years than the three year old coach that you can get for $90-100,000 that needs $2500-3000 for tires, brakes, a few things fixed inside, and does not have a warranty.
In eight years the three year old coach will be eleven years old, the new coach eight years old; that might bring a few thousand dollars more in resale to you. You can't win the depreciation game, it is just how much you want to lose.
