Would you include interconnecting skin in the radiation volume for a patient with lateral forehead squamous cell carcinoma who will receive radiation to the surgical bed and preauricular lymph nodes?

Yes. It's the interconnecting in-transit lymphatics rather than the skin that is the actual target.

Since these are very superficial, an electron field would do the job.

No. Not unless there are dermal mets in which case, you would treat as large a field as possible because dermal mets have no fields. I’ve seen one recurrence above the parotid field and that was in a node just above the field and he has been successfully salvaged.