Many of the larger truck dealerships took a huge hit in 1998 when Ford got out of the over the road truck business. The bulk of their service work was tailored to large profile over the road tractors. When that business disappeared many struggled for years.
The biggest truck Ford currently sells is the F750. It has a much smaller profile than most motorhomes. Rather than waste all the space formerly committed to the large trucks many dealers reconfigured their operations. They tend to focus on the vehicles they sell and tailor their service departments to accommodate them.