Tom, you must have a curved back Scamp. That upper area was changed to a flat back sometime early 1980s and that allows a sliding window. You could always do some fiberglass work and build the area up to put in a sliding window, but other than that.. I don't know how a sliding window would curve to the body... the same goes for the front.
Ten Forward - 2014 Escape 5.0 TA
Double Yolk - 1988 16' Scamp Deluxe