Chassis? Year? Our calipers seized on us at the start of a trip last summer - I couldn't fix it on the side of the road - so $500 at the Ford dealer got us back on the road.
We fixed it last fall by replacing not only the calipers, but the entire motorhome!
Motorhomes tend to sit a lot - and non-use will rust and seize calipers. It seems Fords are especially prone to this issue (right along with a host of other big ticket items).
2016 Forest River Sunseeker 2250SLEC Chevrolet 6.0L