I have removed 3 of my 4 windows
and put them back with a roll of putty from the RV center. Remove a window to see what the core looks like. don't use a coarse blade, to cut a new opening. In my "lil" Bigfoot
; the shell, the insulation and the wall covering is in between the aluminum frames( inside and outside ) as the frame is screwed together the foam insulation is compressed, forcing the putty tape to squeeze out and sealing the window contact surface. The original seal on one of the side windows
was not good for the whole (top) 3" corner radius.