I think RV makers are dropping Ford chassis models as time goes on. Part of it is that they want you to buy a Solera, a Sunseeker MBS, or a Forester MBS. Ford E-350/E-450 B+ rigs are pretty rare, mainly because the RV makers want to push Sprinter based rigs, and I'm guessing if someone wants a longer rig, it is a "C", a gasser "A", or buy used.
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I stand corrected. Looks like Sunseekers and maybe Foresters will have models that have both C cabovers and B+ style overhangs. For example, the 2016 Sunseeker 2430S is a B+.
I think FR may be consolidating their lines, so a Sunseeker can be a "C" or a B+, depending on model type. I know Coachmen does that with their Prism/Prism LE models.