Continuing the process,
After the inside corners have set up, I fit the top and tape it down.
Turn the case upside down and caulk the top.
As you can see, I made 9 cases (7 at 9 x 5, 1 at 17 x 5, 1 at 15 x 5). If they were all 9 x 5, there could have been about 10.5 cases for $35.00. That's less than $3.50 each.
And here's a completed case that I applied diorama asphalt to the base.
I forgot to mention that I try to leave as much of the covering on the plastic as possible. That way there's fewer fingermarks to clean afterwards.