I have built 3 wagon tops and discovered a couple of relatively easy tricks
to improve appearance. I added pieces of .125 x .250 styrene between the
bulkheads, .250 side out, just below the roof curve. This provides
something else to glue to and alleviaties the tendancy of the sides to
buckle inwards. The most important thing I found is that the dimension of
the roof portion of the side from curve to ridge is too much. It is,
therefore a mistake to attach the sides at the roof ridge first and work
down as the extra material has no place to go. I found it best to attach
the sides at the bottom first, after making sure the bend in the sides is
setting correctly on the corner radii of the bulkheads, and then working up.
Then bring the sides together at the roof ridge. You should find that they
do not lay down on the ridge as there is too much material on each side. In
other words, the edges of the side meet before they lay down on the roof
line. This can be corrected by sliding a double sided emory board
lengthwise between the sides until enough material is removed from their
edges so that the sides lay down correctly on the tops of the ends and
bulkheads. This method worked particularly well on the M-15k as it was the
only way I could get the sides to match up correctly with the cutouts in the
side sills.

BTW, by far the toughest Sunshine kit I ever built was a pair of the
insulated 8000 gal tank cars.

Regards,
Bill