I sanded the back of part 1A to remove any debris from the slots and window frames. The sanding stick is held flat on the paper so as to not rip the window frames. Next I used the CA glue. This, if you have never used it, gives the paper an extremely rigid and firm feel to it when the glue sets - which is very quickly. I did this to protect the slim window frames when I was colouring the edges.
Shown here is the glue and the applicator. Just drop it on the paper. Do a trial run if your not sure about using it.