Rating Basis on Motorhome insurance Coverage

I agree with your agent, once a current cash value basis has been established, the insur company does not adjust it unless you request an adjustment. So yes you're paying for a slightly higher rating basis than the actual totaled settlement would be after a few additional yrs depreciation. But you'll be disappointed in how small the premium reduction is for lowering that rating basis.
Many of the annual increases are across the board for an entire state or an area of that state, based on that insurance companies prior year results. It has nothing to do with your record or your policy specifics.