Hi: I have had the door apart on our '77
Boler and taken out the window for re-building. The Boler method was to glass in some strips of plywood across the door in various horizontal places. The Scamp door on the other hand was filled with Buffalo Board ( Tentest) compressed paper board. If the window ever
leaks the Buffalo Board becomes like soggy bread.
A good quality tube of construction adhesive would bond the door skin to an alum. frame!!!
Alf S. North shore of Lake Erie