Insurance declared value of used motor home

I knew you could designate how much liability coverage you wanted but for Collision and Cmprehensive coverage I was always told ACV stood for Actual Cash Value at time of destruction, and whatever the vehicle is worth is what you get paid for on used vehicle. But on new vehicles the insurance companies will insure for Replacement for couple years or so, which means they will pay for a new vehicle.

Maybe I'm not understanding the insurance world like I thought. Really confused now.