Cut the slot in the back of the cabin area for the Cabin supports.For the front trace, the outline and remove the balsa. I like using a Dremel as a router. Using scrap 1/4 x 3/8 u channel spruce you made above, cut some block for attaching the wire to the cabin sides. Mix some 30-min epoxy and attach.Now with the side flat you should be able to insert the spacer blocks (you made when bending the wire above) just under the top as in the photo below.