Forget “Shakespeare in Love.” You want to know the highs and lows of being a writer? ABC hopes to answer this question and more with its upcoming TV movie, “Inside Gilligan’s Island,” based on the 1978 book of the same title by the ’60s sitcom’s creator, Sherwood Schwartz. Variety columnist Army Archerd reports that the film will not focus on the travails of the Professor and Marianne and the other castaways (back when all castaways were funny), but rather on the relationship between Schwartz and his wife Mildred during the course of the show — which has not been off the air since the original episodes ran more than 35 years ago. Schwartz will also executive produce the picture, while son Lloyd will write it. No word yet on casting.