Phil (the OP),
The Ford spark plug problem was solved by 2005. Also, starting in 2005 Ford changed to their TorqShift 5-speed (6 speeds internally) computer controlled transmission in their E350 and E450 chassis that are used under a lot of Class C motorhomes.
I'd recommend staying with 2005 model year on up if it's a Ford chassis you find under a used Class C within you budget.
Our 2005 Itasca and it's Ford chassis is has been excellent regarding build quality, standard features, and options. You might want to locate a 2005 Itasca in the length that meets your needs.