In the TOH instructions, they recommend removing the inside window trim to expose the sash-weight pockets. but after removing part of the trim of several of the windows of my 90-yr old house, there's finished plaster, not a pocket. is this typical, and the TOH guys forgot to mention the step of busting out the plaster before adding the foil-faced rigid foam insulation? or should i just use the unrecommended method of trying to stuff strips of fiberglass insulation in the weight opening of my double-hung windows?